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TEXT-BOOK 


HISTOLOGY 

INCLUDING 

THE  MICROSCOPIC  TECHNIC 

BY 

DR.    PHILIPP   STOHR  * 

PROFESSOR    OF    ANATOMY    AT    THE    UNIVERSITY   OF    WURZBURG 

FIFTH  AMERICAN  FROM  THE  TENTH  GERMAN  EDITION 
TRANSLATED  BY  DR.   EMMA  L.    BILSTEIN 

FORMERLY   DIRECTOR  OF  THE   LABORATORIES  OF   HISTOLOGY  AND   EMBRYOLOGY,  WOMAN'S  MEDICAL 

COLLEGE   OF   PENNSYLVANIA 

EDITED,  WITH  ADDITIONS 

BY 

DR.    ALFRED    SCHAPER 

PROFESSOR   OF   ANATOMY,    UNIVERSITY    OF    BRESLAU  ;    FORMERLY   ASSISTANT    PROFESSOR    OF    HISTOLOGY 

HARVARD    MEDICAL   SCHOOL,    BOSTON,    MASS.;    FORMERLY    DOCENT    OF   ANATOMY   AND   FIRST 

ASSISTANT   AT   THE   ANATOMICAL    INSTITUTE   OF   THE   UNIVERSITY   OF   ZURICH 

Witb  353  miustratious 


PHILADELPHIA 

P.   BLAKISTON'S   SON    &   CO. 

IOI2     WALNUT    STREET 
1903 


Copyright,   1903,  by  Dr.  Alfred  Schaper. 


If03 


WM.     F.     FELL     COMPANY 

eUECTROT  YPERS,  PRIN7EF:! 

PHILADELPHrA,     PA. 


EDITOR'S  PREFACE  TO  THE   FIFTH  EDITION 


This  edition  has  been  revised  in  accordance  with  the  tenth  German 
edition,  and  presents  much  that  is  new,  both  in  revision  of  the  former 
text  and  additions  throughout  the  entire  work.  Among  the  most  im- 
portant changes  are — 

Fifty  new  illustrations,  a  number  in  colors,  and  new  color  schemes 
of  the  Spleen,  Lung,  Kidney,  and  Retina. 

Five  new  chapters  upon  the  following  subjects  : 

The  Form  of  Glands,  based  on  the  investigations  of  Maziarski. 

The  Spleen,  based  on  the  researches  of  Weidenreich, 

The  Urinary  Bladder,  based  on  the  researches  of  Lendorf. 

The  Seminal  Passages,  based  on  the  researches  of  Felix. 

The  Development  of  the  Hairs,  based  on  the  author's  own  re- 
searches. 

There  are,  besides,  many  lesser  alterations  and  additions,  including 
the  latest  investigations  on  the  Morphology  of  the  Cell  and  the  Struc- 
ture and  Chemistry  of  the  Tissues  ;  also  the  addition  to  the  technical 
part  of  the  application  of  Formol  and  its  mixtures. 

The  editor  acknowledges  gratefully  the  appreciation  of  Professor 
Stohr's  work  shown  by  many  teachers  and  students,  and  trusts  that  this 
new  edition  may  yet  increase  its  usefulness. 

Alfred  Schaper. 
Breslau,  August,  igo^. 


Ill 


EDITOR'S  PREFACE  TO  THE  FIRST  EDITION, 


Stohr's  text-book  is  well  known  to  the  histologists  of  all  nations  and 
held  in  high  esteem  by  them.  To  the  German  medical  student  it  has 
become  an  indispensable  guide.  During  the  ten  years  of  its  existence  it 
has  reached  an  extraordinary  sale  and  passed  through  six  revised  editions. 
It  has  been  translated  into  Italian  (1887),  French  (1890),  and  Russian 
( 1 89 1 ),  and  has  thus  come  into  the  hands  of  the  students  of  these  nations. 
These  facts  are  sufficient  to  guarantee  the  value  of  the  work  without 
further  recommendation.  Although  excellent  text-books  of  Histology 
already  exist  in  English,  still  the  peculiarity  and  special  superiority  of 
Stohr's  text-book  justifies,  in  our  opinion,  its  translation  into  English  for 
the  convenience  of  American  and  English  students.* 

It  is  especially  intended  for  the  use  of  students,  but  even  profes- 
sional histologists  and  physicians  will  find  in  it  much  valuable  informa- 
tion, as  well  as  suggestions  for  technical  purposes.  The  chief  merit  of 
the  work  lies,  on  the  one  hand,  in  the  brevity  and  perspicuity  of  the 
descriptive  text,  elucidated  by  illustrations  which  have  thus  far  never 
been  excelled  ;  and,  on  the  other  hand,  in  the  simplicity  and  certainty 
of  the  methods  for  preparing  the  most  important  microscopical  speci- 
mens. The  young  student  is  thus  enabled  to  practice  histological 
methods  privately,  at  a  minimum  cost,  in  connection  with  his  courses  in 
the  university.  The  preparation  of  almost  all  of  the  specimens  enu- 
merated in  the  book  can  be  made  simply  by  means  of  teasing,  isolation, 
or  cutting  with  the  razor,  but  those  students  who  have  a  microtome  at 
their  disposal  will  also  find,  in  an  Appendix,  brief  directions  for  the  pre- 
paratory treatment  (embedding  in  paraffin  and  celloidin)  of  specimens 
for  sectioning  with  the  microtome. 

With  the  permission  of  Prof  Stohr  we  have  made  several  imma- 
terial, but  for  an  American  edition  very  desirable,  changes  in  the  text, 
and  have  considered  it  preferable  to  place  the  technical  part  as  a 
whole  at  the  end  of  the  book  rather  than  in   sections  after  the  several 

*  In  1888  Stohr's  text-book  was  utilized  in  Kendrick's  Physiology,  but  in  such  a  frag- 
mentary form  and  so  intermingled  with  selections  from  other  authors  that  its  chief  merits  were 
entirely  lost.     This  use  of  the  book  can  not  be  considered  as  an  English  translation  proper. 

V 


VI  EDITOR  S    PREFACE    TO    THE    FIRST    EDITION. 

chapters.  Furthermore,  we  have  enlarged  the  chapter  on  the  Uterus,  in 
order  to  give  detailed  consideration  to  the  various  functional  conditions 
of  the  organ,  and  added  to  the  book  an  entirely  new  chapter  on  the 
Placenta.  Eight  new  illustrations  (Figs.  229,  230,  232,  233,  234,  236, 
237,  238)  were  necessary  for  these  additions. 

The  editor  is  under  great  obligation  to  the  translator,  Dr.  Billstein, 
for  her  successful  efforts  in  reproducing  the  conciseness  and  clearness  of 
the  German  original.  Further,  he  desires  to  express  his  gratitude  to  Prof. 
Philipp  Stohr  for  placing  at  his  disposal  the  original  electrotypes,  and  to 
Drs.  Bohm  and  von  Davidoff  for  the  illustration  of  the  virginal  uterus 
(Fig.  229)  from  their  "  Lehrbuch  der  Histologic."  He  also  feels  deeply 
indebted  to  Prof.  Charles  S.  Minot  for  kind  assistance,  for  valuable  criti- 
cism, and  for  permission  to  use  two  illustrations  (Figs.  231  and  234)  from 
his  text-book  of  "  Human  Embryology  "  ;  and,  finally,  to  Messrs.  P, 
Blakiston,  Son  &  Co.,  Philadelphia,  for  the  very  satisfactory  reproduction 
of  the  new  drawings,  and  for  their  many  courtesies  during  the  prepara- 
tion of  the  American  edition. 

Alfred  Schaper. 
Harvard  Medical  School, 
Boston,  June,  i8g6. 


CONTENTS 


PART  I. 


GENERAL  TECHNIC. 


I.  The    Laboratory    Appoint- 
ments,     

Instruments. 
Reagents. 

II.  The  Preparation  of  Micro- 
scopic Specimens,  .... 

Introduction. 

Nature  of  the  Material. 

Killing  and  Dissecting  the  Ani- 
mals. 

Isolation. 

Fixation. 

Hardening. 

Decalcitication. 


PAGE 

17-26 


27-54 


The  Preparation  of  Microscopic  Spec- 
imens. —  Continued. 

Sectioning. 

Staining. 

Injecting. 

Mounting  and  Preserving  of  the 
Preparations. 

Examination  of  Fresh  Objects. 

Storing  of  Permanent  Speci- 
mens. 

III.  Management  of  the  Micro- 
scope,      

Sketching. 
Measurement. 


55-59 


PART  II. 

MICROSCOPIC  ANATOMY  AND  SPECIAL  TECHNIC. 

I.   HISTOLOGY. 
(Microscopic  .\natomy  of  the  Cells  and  the  Tis-iues.) 
63-75       Tissues. — Continued. 


A. — The  Cells, 

Parts  of  the  Cell. 

Form  of  Cells. 

Size  of  Cells. 

Vital  Properties  of  Cells. 

Phenomena  of  Motion  in  Cells. 

Reproduction  and  Multiplication 
of  Cells. 

Phenomena  of  Secretion  in  Cells. 

Duration  of  the  Life  of  Cells. 

Growth  of  Cells. 

Secretory  Products  of  Cells. 

Union  of  Cells. 

Technic  No.  i, 73-75 

B. — The  Tissues, 75-125 

I.  The  Epithelial  Tissues,    .    .         75-8S 
Secretory  Activity  of  Epi- 
thelial Tissue. 


The  Glands. 

Technic  No.  2,  3,     ...    .  88 

II.   The    Supporting  Tissues,    .    .       89-104 
Connective  Tissue. 
Cartilage. 
Osseous  Tissue. 
Technic  No.  4-20,    ....     101-104 

III.  The  Muscle  Tissues,     ....     104-112 

Smooth  Muscle  Tissue. 

Cardiac  Muscle. 

Striated  Muscle  Tissue. 

Technic  No.  21-27,  ....     no— 112 

IV.  The  Nerve  Tissues, 112-125 

Nerve-cells. 

Nerve-fibers. 

Technic  No.  28-36 122-125 


VUl 


CONTENTS. 


II.   MICROSCOPIC  ANATOMY  OF  THE  ORGANS. 


I.  Organs    of    the    Circula-  page 

TORY  System, 126-159 

1.  The    Blood-vessel    System,   126-140 
The  Heart. 

The  Arteries. 
The  Veins. 
The  Capillaries. 

Development    of    Capil- 
laries. 
Glomus  caroticum  and  coc- 

cygeum. 
The  Blood. 

Development  of   Colored 

Blood  Corpuscles. 
Development  of  Colorless 
Blood  Corpuscles. 

2.  The  Lymph-vessel  System,     141-152 
The  Lymph-vessels. 

The  Lj'mph-glands. 

The      Peripheral      Lymph- 
nodules. 

The  Lymph. 
The  Spleen. 
Technic  No.  37-60,      ....     152-159 

II.  Organs   of   the   Skeletal 

System, 159-181 

The  Bones. 

The  Articulations  of  Bones. 
The  Cartilages. 
The     Development      of    the 
Bones. 
Development    of    Primary 

Bone. 
Development   of    Second- 
ary or  Connective-tissue 
Bone. 
The  Growth  of  Bones. 
The  Resorption  of  Bones. 
Technic  No.  61-67, 177-181 

III.  Organs  of    the  Muscular 

System,    182-187 

The  Muscles. 
The  Tendons. 
The  Fascire. 

Tendon-sheaths  and  Bursre. 
Technic  No.  68-72,      ....     185-1S7 

IV.  Organs   of    the    Nervous 

System,     187-238 

I.  The  Central  Nervous  System,   187-211 


Organs    of  the    Nervous    System. —         page 
Contimied. 
The  Spinal  Cord. 
Topography. 
Minute  Structure. 
The  Brain. 

The  Cerebral  Cortex. 
The  Cerebral  Ganglia. 
The  Gray  Substance  of 

the  Ventricles. 
The  Cerebellar  Cortex. 
The  "White  Substance. 
The  Hypophysis   Cere- 
bri. 
The  Epiphysis. 
The    Membranes   of    the 
Central     Nervous     Sys- 
tem. 
The  Vessels  of  the  Cen- 
tral Nervous  System. 
2.  The    Peripheral    Nervous 

System, 212-227 

The  Nerves. 
The  Ganglia. 

The  Peripheral  Nerve- end- 
ings. 
Terminations  of  Sensory 

Nerves. 
Terminations   of  Motor 
Nerves. 
The  Suprarenal  Body,     .    .    .    227-230 
Technic  No.  73-95,     ....    230-238 

V.  The  Digestive  Organs,    .    239-307 
The  Mucous  Membrane. 

A.  Headgut. 
The  Oral  Cavity. 

The  Mucous  Membrane  of 

the  Oral  Cavity. 
The  Glands   of  the    Oral 

Cavity. 
The  Teeth. 

Development  of  the  Teeth. 
The  Tongue. 
The  Soft  Palate    and   the 

Pharynx. 

B.  Rumpgut. 
The  Foregut. 

The  Esophagus. 
The  Stomach. 
The  Midgut. 


CONTENTS. 


The  Digestive  Organs.  —  Continued . 
The   Duodenum    and    the 
Small  Intestine. 

The  Endgut. 

The  Large  Intestine. 
The  Rectum. 

The  Lymph-nodules  of  the 
Stomach  and  the  Intes- 
tines. 

The  Blood-vessels  of  the 
Stomach  and  the  Intes- 
tines. 

The  Lymph -vessels  of  the 
Stomach  and  the  Intes- 
tines. 

The  Nerves  of  the  Stomach 
and  the  Intestines. 

The  Pancreas. 

The  Liver. 

The  Peritoneum. 

Technic  No.  96-127,    .    .    .     296-307 

VI.  The  Respiratory  Organs,    308-321 
The  Larynx. 
The  Trachea. 

The  Bronchi  and  the  Lungs. 
The  Thyroid  Gland. 
The  Thymus. 
Technic  No.  128-133,  •    •    •     319-321 

vn.  TheUrinary Organs,  .    .    321-335 
The  Kidneys. 
The  Urinary  Passages. 
The    Renal    Calices.    Renal 
Pelvis,  and  Ureter. 
The  Bladder. 
The  Urethra. 
Technic  No.  I34-I43>      •    •     333-335 

VIII.  The  Reproductive  Organs,  336-372 
The  Male  Reproductive  Or- 
gans. 

The  Testes. 
The  Semen. 
The  Seminal  Passages. 
Accessory  Glands  of  the 
Male  Sexual  Organs. 
The  Penis. 
The    Female     Reproductive 
Organs. 

The  Ovaries. 

The  Epoophoron  and 
the  Paroophoron. 


The     Reproductive    Organs.  —  Con- 
tinned. 
1  he  Oviduct. 
Tiie  Uterus. 
The  Placenta. 
The  Vagina  and  the  Ex- 
ternal   Female    Geni- 
talia. 
Technic  No.  144-160,  .    .    .     369-372 

IX.  The  Skin 373-398 

The  External  Skin. 
The  Nails. 

The  Hairs  and  the  Hair-Fol- 
licles. 
The    Development    of    the 
Hairs. 
Growth  of  the  Hair  and  of 

the  Root-sheaths. 
Shedding  and  Renewal  of 
Hair. 
The  Glands  of  the  Skin. 
The    Blood-vessels,  Lymph- 
vessels,  and  Nerves  of  tlie 
Skin. 
The  Mammary  Gland. 
Technic  No.  161-176,  .    .    .     395-398 

X.  The  Organ  of  Vision,  .    .    398-436 
The  Eyeball. 
The  Tunica  Externa. 

The  Cornea. 

The  Sclera. 
The  Tunica  Media. 

The  Choroid. 

The  Ciliary  Body. 

The  Iris. 
The  Angle  of  the  Iris. 
The  Tunica  Interna. 

1.  Pars  Optica  Retinae. 
The  Cerebral  Layer. 
The     Neuro- epithelial 

Layer. 

The  Pigmented  Epithe- 
lium. 

The  Macula  and  Fovea 
Centralis. 

The  Ora  Serrata. 

2.  Pars  Ciliaris  Retinae. 

3.  Pars  Iridica  Retince. 
The  Optic  Nerve. 

The  Lens. 

The  Vitreous  Body. 


CONTENTS. 


The   Organ  of  Vision. — Coiitiiuied. 

The  Zonula  Ciharis. 

The  Blood-vessels  of  the  Eye- 
ball. 

The  Lymph-paths  of  the 
Eyeball. 

The  Nerves  of  the  Eyeball. 

The  Eyelids. 

The  Lacrimal  Organ. 

Technic  No.  177-192,      .    . 

XL  The  Organ  of  Hearing,  . 
The  Internal  Ear. 

The  Saccule,  the   Utricle, 
and     the     Semicircular 
Canals. 
The  Cochlea. 


429-436 


436-453 


The  Organ  of  Hearing. — Conti7iiied. 
The  Middle  Ear. 

The  Tympanic  Cavity. 
The  Eustachian  Tube. 
The  External  Ear. 
The  Tympanum. 
The     External     Auditory 
Meatus. 
Technic  No.  193-19S,  .    .    .     450-453 

XII.  The  Olfactory  Organ,  .    453-458 
The  Vestibular  Region. 
The  Respiratory  Region. 
The  Olfactory  Region. 
Technic    No.  199-202,     .    .     457-458 

XIII.  The  Gustatory  Organ,    .    458-461 
Technic  No.  203-205,  .    .    .  461 


APPENDIX. 


Microtome  Technic, 463- 

I.  The  Microtome. 
II.    Embedding. 

The  Paraffin  Method. 
The  Celloidin  Method. 
III.   Sectioning. 

Paraffin  Objects. 

With   the   knife   placed 

obliquely. 
With   the    knife    placed 
transversely. 


Microtome  Technic. — Continued. 

Obstacles  in  Sectioning 
and  their  Remedy. 
Celloidin  Objects. 
IV.   Preservation  of  Sections. 
Paraffin  Objects. 
Celloidin  Objects. 

Books   Recommended  for   Col 
lateral  Study, 

Index, .    . 


471 
473 


LIST  OF  ILLUSTRATIONS. 


FIG.  •  PAGE 

1.  Leitz  Microscope, 5^ 

2.  Schematic  Section  of  the  Body  of  a  Vertebrate  Embryo, 60 

3.  Scheme  of  a  Cell, 64 

4.  Epithelium  of  the  Large  Intestine, 65 

5.  Marrow  Cell  of  a  Rabbit,          66 

6.  Leucocytes  of  a  Frog, 67 

7.  Scheme  of  the  Close  Coil, 69 

8.  Scheme  of  the  Loose  Coil, 69 

9.  Scheme  of  the  Mother  Star, 70 

10.  Scheme  of  Metakinesis, 70 

11.  Scheme  of  the  Daughter  Stars,     .    .  ' 7^ 

12.  Scheme  of  Cell  Division,                                7^ 

13.  Nuclear  Structure,  Connective-tissue  Cell, 74 

14.  Karyokinetic  Figures,         74 

15.  Epithelial  Cells  of  a  Rabbit,  Isolated, 75 

16.  Pigmented  Epithelium  of  the  Retina, 76 

17.  Simple  Cylinder  Epithelium, 76 

18.  Stratified  Squamous  Epithelium, 76 

19.  Scheme  of  a  Many-rowed  Epithelium, 77 

20.  Many-rowed  Ciliated  Epithelium, 7^ 

21.  Terminal  Bars,  Cylinder  Epithelium, 78 

22.  Scheme  of  the  Network  of  Terminal  Bars, 78 

23.  Prickle-Cells,      ......' 79 

24.  Serous  Gland-Cells, 80 

25.  Secreting  Epithelial  Cells, 80 

26.  Crypt  of  Lieberkiihn, 82 

27.  Schemes  of  Tubular  Gland  Forms, S^ 

28.  Schemes  of  Alveolo-Tubular  Gland  Forms,           84 

29.  Schemes  of  Alveolar  Gland  Forms, 84 

30.  Mucous  Gland  of  the  Tongue  of  a  Rabbit, 85 

31.  Schematic  Model  of  a  Human  Fundus  Gland 86 

32.  Schematic  drawing  of  the  different  divisions  of  a  Gland, 87 

33.  Mucous  Connective  Tissue  from  the  Umbilical  Cord, 89 

34.  Connective-Tissue  Bundles, 90 

35.  Elastic  Fibers, 91 

36.  Network  of  Elastic  Fibers,  passing  into  a  Fenestrated  Membrane, 91 

37.  Connective-Tissue  Cells,  Connective-Tissue  Bundles,  Plasma  Cells, 92 

38.  Fat-cells, 92 

39.  Adipose  Tissue,      93 

40.  Serous  Fat-Cells, 93 

41.  A  Piece  of  the  Greater  Omentum  of  Man, 94 

42.  Reticular  Connective  Tissue, 95 

43.  Hyaline  Cartilage,  Ensiform  process  of  a  Frog, 96 

44.  Human  Costal  Cartilage, 96 

45.  Elastic  Cartilage,    ...             97 

46.  Section  of  an  Invertebral  Disk  of  Man, 9<^ 

47.  Ground  Section  of  Dried  I>one  of  adult  Man, 99 

48.  Section  of  the  Osseous  Turbinal  of  adult  Man, 99 

49.  Section  of  the  Diaphysis  of  the  Humerus  of  a  human  Embryo, 99 

50.  Adipose  Tissue, ■ 102 

51.  Smooth  Muscle-Fibers, 105 

52.  Transverse  Section  of  Smooth  Muscle- Fibers, 105 

53.  Muscle-Fibers  of  the  Heart, 106 

54.  Striated  Muscle-Fibers  of  Man, .    •  107 


Xll  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

55.  Transverse  Section  of  human  Striated  Muscle- Fibers, 108 

56.  Isolated  Striated  Muscle-Fibers  of  a  Frog, 108 

57.  Apparent  Intercellular  Bridges  of  Smooth  Muscle-Fibers, iio 

58.  Diagram  of  a  Neuron, 1 13 

59.  Different  Forms  of  Nerve-Cells, 114 

60.  Multipolar  Nerve-Cells, 115 

61.  Ganglion  Cell  with  Nissl's  Bodies, 115 

62.  Ganglion  Cell  with  Trophospongium,        115 

63.  Ganglion  Cell  with  Apparato  Reticulare,      IIS 

64.  Cell  of  Purkinje, II6 

65.  Nerve-Cell  from  the  Spinal  Cord  of  a  human  Embryo, I17 

66.  Teased  Preparation  of  the  Sympathetic  Nerve  of  a  Rabbit, 119 

67.  Medullated  Nerve-Fibers, .• 120 

68.  Medullated  Nerve-Fibers,  treated  with  Silver  Nitrate I2[ 

69.  Nerve-Fiber,  showing  a  Node  of  Ranvier,  .    .             124 

70.  Transverse  Section  of  a  Papillary  Muscle  of  a  human  Heart, 127 

71.  Longitudinal  Section  of  a  Papillary  Muscle  of  a  human  Heart, 127 

72.  Small  Arteries  of  Man, 129 

73.  Epithelium  of  a  Mesenteric  Artery, 129 

74.  Cross-Section  of  the  Brachial  Artery  of  Man,      130 

75.  Cross-Section  of  the  Thoracic  Aorta  of  Man, 131 

76.  Cross-Section  of  a  human  Vein, 133 

77.  Elastic  Fibers  of  a  human  Vein, 133 

78.  Section  of  the  Renal  Vein  of  Man.       134 

79.  Developing  Capillaries  in  the  Omentum  of  a  Rabbit, 135 

80.  Human  Blood  Corpuscles ;  Amphibian  Blood  Corpuscles 137 

81.  Colorless  Blood-Cells  of  Man, 137 

82.  Hemin  and  Hematoidin  Crystals  of  Man;    Hemoglobin  Crystals  of  a  Dog,    ....  140 

83.  Lymph-Vessel  from  the  Mesentery  of  a  Rabbit, 141 

84.  Longitudinal  Section  of  a  human  Cervical  Lymph-Gland, 142 

85.  Section  of  a  Lymph-Gland  of  a  Rabbit, 144 

86.  Section  of  the  Medulla  of  a  Lymph-Gland  of  an  Ox, I4S 

87.  Section  of  the  Medulla  of  a  Lymph-Gland  of  an  Ox, 145 

88.  Scheme  of  the  human  Spleen,        147 

89.  Section  of  the  Injected  Spleen  of  a  Cat,  .    .    .  • 148 

90.  Cross-Section  of  a  human  Spleen,      149 

91.  Elements  of  the  human  Spleen, I49 

92.  Reticular  Connective  Tissue  of  the  human  Spleen, 149 

93.  Thin  Section  of  a  human  Spleen,      150 

94    Section  of  the  Spleen  of  a  Mouse,  showing  nerves, IS'' 

95.  Longitudinal  Section  of  a  human  Metacarpus, 160 

96.  Cross-Section  of  a  human  Metacarpus, l6l 

97.  Elements  of  human   Bone-Marrow,           162 

98.  Section  of  the  Bone-Marrow  of  a  Rabbit, 163 

99.  Cross-Section  of  the  Femur  of  an  adult  Man,  .                          164 

100.  Vertical  Section  of  the  Head  of  a  Metacarpus  of  adult  Man, 1 66 

loi.   Synovial  Villi  from  a  human  Knee-joint, 167 

102.  Longitudinal  Section  of  a  Phalanx  of  the  Little  Finger  of  a  human  Fetus,  ....  169 

103.  Dorso-Palmar  Section  of  a  Middle-Finger  Phalanx  of  a  human  Fetus, 170 

104.  Longitudinal  Section  of  the  Phalanx  of  the  first  Finger  of  a  human  Embryo,     .    .    .  171 

105.  Section  of  the  upper  half  of  the  Shaft  of  the  Humerus  of  a  human  Embryo,     .    .    .  172 

106.  Section  of  the  Hard  Palate  of  a'  Kitten >73 

107.  Section  of  the  Inferior  Maxilla  of  a  human  Fetus, 175 

108.  Ostoclasts  and  Howship's  Lacunae,    ...             176 

109.  Elements  of  the  fresh  Bone-Marrow  of  a  Calf, 179 

no.   Cross-Section  of  the  Omo-Hyoid  Muscle  of  Man, 182 

III.  Portion  of  Figure  no  more  highly  Magnified, 183 

1X2.   Cross-Section  of  human  Tendon, 184 

113.  Tendons  of  a  Rat's  Tail, 184 

114.  Section  of  the  Gastrocnemius  Muscle  of  a  Frog, 184 

115.  Cross-Section  of  the  human  Spinal  Cord,              188 

1x6.   Motor  Nerve-Cells  from  the  Spinal  Cord  of  a  Rabbit, 190 

117.  Cross-Section  of  the  Spinal  Cord  of  an  Embryo  Chick, 191 

118.  Scheme  of  the  Spinal  Cord, 192 

XI9.    Longitudinal  Section  of  the  Spinal  Cord  of  a  Rat, 193 

120.   Section  of  the  Spinal  Cord  of  a  Rat,  showing  Collaterals, 194 


LIST    OF    ILLUSTRATIONS.  Xlll 

FIG.  PAGE 

121.  Glia-Cells  from  tbe  Spinal  Cord, 196 

122.  Section  of  ihe  Lateral  Column  of  a  human  Spinal  Cord, 197 

123.  Vertical  Section  of  the  human  Cerebral  Cortex, 199 

124.  Scheme  of  the  Cerebral  Cortex, 199 

125.  Pyramidal  Cell  from  the  Cerebral  Cortex  of  adult  Man, 200 

I2t).   Glia-Cells  from  the  Brain  of  Man,         201 

127.  Section  of  the  Cerebellum  of  adult  Man,      203 

128.  Small  Granule-Cell  from  the  Cerebellar  Cortex  of  a  Kitten,      204 

129.  Large  Granule-Cell  from  the  Cerebellar  Cortex  of  a  Kitten, 204 

130.  Scheme  of  the  Cerebellar  Cortex, 205 

131.  Basket-Cell  of  the  Cerebellar  Cortex  of  a  Cat, 206 

132.  Small  Cortical  Cell  from  the  human  Cerebellum, 207 

133.  Glia-Cells  of  the  Cerebellar  Cortex  of  adult  Man,       ....  207 

134.  Section  of  a  human  Pituitary  Body, 208 

135.  Acervulus  Cerebri  from  a  human  Pineal  Body, 209 

136.  Elements  of  the  Gray  Substance  of  the  wall  of  a  Ventricle  of  the  human  Brain,    .    .  209 

137.  Portion  of  the  Plexus  Chorioideus  of  adult  Man, 210 

138.  Cross-Section  of  a  human  Median  Nerve, 212 

139.  Cross-Section  of  a  human  Median  Nerve, 213 

140.  Longitudinal  Section  of  a  Spinal  Ganglion  of  a  Calf, 214 

141.  Cross-Section  of  the  Gasserian  Ganglion  of  Man, 215 

142.  Scheme  of  the  Nervous  Elements  of  a  Spinal  Ganglion, 216 

143.  Scheme  of  the  Elements  of  Two  Sympathetic  Ganglia, 218 

144.  Tactile  Corpuscle,  Cells  of  Langerhans,  Intraepithelial  Nerve-Fibers, 220 

145.  Tactile  Cells  in  a  Section  of  the  Skin  of  a  human  Toe, 221 

146.  Compound  Tactile-Cells  from  the  Cere  of  a  Goose, 222 

147.  Cylindrical  End- Bulb  from  the  Conjunctiva  of  a  Calf, 223 

148.  Lamellar  Corpuscle  from  the  Mesentery  of  a  Cat, 223 

149.  Tactile  Corpuscle  from  a  Section  of  a  human  Toe, 224 

150.  Tendon  Spindle  of  a  Cat, 225 

151.  Portion  of  Plgure  150  more  highly  magnified, 225 

152.  Muscle-Spindle  of  a  Cat,                          226 

153.  Motor  Nerve-Endings  of  the  Intercostal  Muscles  of  a  Rabbit, 227 

154.  Motor  Nerve-Ending  in  an  Ocular  Muscle-Fiber  of  a  Rabbit, 227 

155.  Section  of  a  human  Suprarenal   Body, 228 

156.  Section  of  a  human  Suprarenal  Body, 228 

157.  Section  through  Cortex  and  Medulla  of  the  Suprarenal  Body  of  adult  Man,  ....  229 

158.  Section  of  a  human  C^erebral  Cortex, 232 

159.  Transverse  Section  of  a  Peripheral  Spinal  Nerve, 234 

160.  Section  of  the  Mucous  Membrane  of  the  Lip  of  Adult  Man, 240 

161.  Tubules  of  Lingual  Glands, , 241 

162.  Serous  Gland  of  a  Mouse,       .        242 

163.  Scheme  of  the  human  Parotid  Gland, 243 

164.  Section  of  the  Parotid  Gland  of  Man, 243 

165.  Scheme  of  the  human  Sublingual  Gland, 244 

166.  Section  of  the  Sublingual  Gland  of  Man, 245 

167.  Scheme  of  the  human  Submaxillary  Gland, 246 

168.  Section  of  the  Submaxillary  Gland  of  Man, .  247 

169.  Demilunes  and  Secretory  Capillaries  of  the  Submaxillary  Gland, 247 

170.  Longitudinal  Section  of  a  human  Incisor  Tooth, 248 

171.  Longitudinal  Section  of  a  human  Molar  Tooth, 249 

172.  Longitudinal  Section  of  the  Fang  of  a  human  Molar  Tooth, 249 

173.  Enamel  Prisms,  isolated, 250 

174.  Enamel  Prisms  in  Transverse  Section 250 

175.  Six  Odontoblasts  with  Dental  Fibers, 250 

176.  Schematic  Representation  of  the  Initial  Processes  in  the  Development  of  the  Teeth,  251 

177.  Frontal  Section  of  the  Head  of  an  Embryo  Sheep, 251 

178.  Section  of  the  Lower  Jaw  of  a  human  Embryo,      252 

179.  Section  of  the  Upper  Jaw  of  a  human  Embryo, 252 

180.  Section  of  a  Developing  Tooth  of  a  human  Fetus, 253 

181.  Section  of  a  Milk-Tooth  of  a  newborn  Dog, 254 

182.  Section  of  an  Incisor  Tooth  of  a  Kitten,      255 

183.  Filiform  Papillre  of  the  human  Tongue, 257 

184.  Fungiform  Papilla  of  the  human  Tongue, .    .  257 

185.  Vertical  Section  of  a  Vallate  Papilla  of  Man, 258 

186.  Vertical  Section  of  a  Lingual  Tonsil  of  adult  Man, 259 


XIV  LIST    OF    ILLUSTRATIONS. 

FIG.              ....                                                      ,  PAGE 

187.   Thin  Section  of  a  I-ingual  Tonsil  of  Man,  .    .    .    .   ' 260 

lUS.  Transverse  Section  of  the  Upper  Third  of  the  human  Esophagus, 263 

189.  Section  of  the  Middle  Third  of  the  human  Esophagus 264 

190.  Transverse  Section  of  a  human  Stomach,              .         .     .    .    .    ,         ,  265 

191.  Vertical  Section  of  the  Mucous  Membrane  of  a  human  Stomach, 266 

192.  Transverse  Section  of  a  human  Fundus  Gland, 267 

193.  Section  of  a  human  Gastric  Mucous  Membrane, 268 

194.  Section  of  the  human  Pyloric  Mucous  Membrane, 269 

195.  Section  of  the  Jejunum  of  adult  Man, 270 

196.  Section  of  the  Mucous  Membrane  of  the  Jejunum  of  adult  Man,          271 

197.  Intestinal  Crypts,  Cells  of  Paneth, 272 

198.  Intestinal  Epithelium, , 273 

199.  Longitudinal  Section  of  the  Apex  of  a  Villus  of  a  Dog, 273 

200.  Longitudinal  Section  of  the  Duodenum  of  Man, 274 

201.  Section  of  Duodenal  Glands, 274 

202.  Mucous  Membrane  of  the  Descending  Colon  of  Man, 276  . 

203.  Transverse  Section  of  a  patch  of  Peyer  of  the  Small  Intestine  of  a  Cat, 277 

204.  Crest  of  a  Solitary  Nodule  from  the  Small  Intestine  of  a  Kitten, 278 

205.  Section  of  the  Injected  Small  Intestine  of  Man, 279 

206.  Plexus  Myentericus  and  Plexus  Submucosus  of  an  Infant, 281 

207.  Scheme  of  the  human  Pancreas, 282 

208.  Sections  of  the  Pancreas  of  Man, 282 

209.  Gland-Tubule  of  the  Pancreas  of  Necturus,  shov^'ing  Zymogen  Granules, 283 

210.  Intercellular  Secretory  Capillaries  of  the  human  Pancreas, 283 

211.  Scheme  of  an  ordinary  Compound  Tubular  Gland,      ,        284 

212.  Scheme  of  the  Liver, 284 

213.  Scheme  of  an  End- piece  of  a  Tubular  Gland, 285 

214.  Scheme  of  an  End-piece  of  the  Liver,      285 

215.  Section  of  a  Rabbit's  Liver, 286 

216.  Scheme  of  an  Hepatic  Lobule, 287 

217.  Section  of  a  human  Liver,      288 

21 S.    Section  of  a  human  Hepatic  Lobule,  showing  Bile  Capillaries, 289 

219.  Bile  Capillaries,  silvered  after  Golgi, 290 

220.  Bile  Capillaries,  injected, 290 

221.  Section  of  the  Liver  of  a  Dog,  after  Golgi, 291 

222.  Liver  Cells  of  Man, 292 

223.  Horizontal  Section  of  the  Injected  Liver  of  a  Rabbit, 292 

224.  Horizontal  Section  of  the  Injected  Liver  of  a  Cat, 292 

225.  Portal  Capillaries  and  Bile  Capillaries,  injected,       293 

226.  Vertical  Section  of  the  Injected  Liver  of  a  Cat, 293 

227.  Lattice-Fibers  of  the  human  Liver, 294 

228.  Greater  Omentum  of  a  Rabbit, 295 

229.  Isolated  Fundus  Gland  of  a  Rabbit, 300 

230.  Intestinal  Villus  of  a  Rabbit, 301 

231.  Intestinal  Crypts  of  a  Rabbit, 303 

232.  Gland-Cells  of  the  Pancreas, 305 

233.  Intralobular  Connective  Tissue  of  the  Liver,       306 

234.  Scheme  of  the  human  Bronchial  Tree, 310 

235.  Section  of  a  Bronchiole  of  a  Child, ......  31 1 

236.  Section  of  a  Lung  of  adult  Man, 312 

237.  Respiratory  Epithelium  of  a  human  Lung,  ...         313 

238.  Section  of  Lung  of  a  Rabbit,  showing  Elastic  Fibers,    ....             314 

239.  Section  of  the  Lung  of  a  Child,  Injected  through  the  Pulmonary  Artery,  ....  315 

240.  Section  of  the  Thyroid  Gland  of  adult  Man 316 

241.  Section  of  the  Thymus  of  a  Rabbit  seven  days  olH, 317 

242.  Section  of  the  Thymus  of  a  Child  21  months  old, 318 

243.  Corpuscle  of  Hassal,           318 

244.  Scheme  of  the  Course  of  the  Uriniferous  Tubules  and  the  Renal  Blood-vessels,    .    .  322 

245.  Section  of  Human  Kidney,  showing  boundary  between  cortex  and  medulla,       .    ,    .  323 

246.  Scheme  of  a  Renal  Corpuscle, 324 

247.  Section  of  a  human  Kidney,  showing  a  Renal  Corpuscle, 325 

248.  Tubules  of  a  Medullary  Ray, 325 

249.  Transverse  Section  of  a  Renal  Papilla, 325 

250.  Section  through  the  Cortex  of  a  human  Kidney, 326 

251.  Transverse  Section  through  the  Medulla  of  a  human  Kidney, 326 

252.  Longitudinal  Section  of  the  Injected  Kidney  of  a  Guinea-Pig, 327 


LIST    OF    ILLUSTRATION'S.  XV 

FIG.  PAGE 

253.  Nerve  Ple.xus  in  a  Section  of  the  Kidney  of  a  Mouse, 328 

254.  Transverse  Section  of  the  Lower  Half  of  a  liuman  Ureter, 329 

255.  Vertical  Section  of  a  human  Vesical  Mucous  Membrane, .    .  330 

256.  Section  of  the  Fundus  of  the  Urinary  Bladder  of  Man, 33I 

257.  Isolated  Uriniferous  Tubules, ...             ...  334 

258.  Section  of  the  Testis  of  a  newborn  Child, 336 

259.  Section  of  the  Testis  of  an  Ox,                    337 

260.  Section  of  the  Testis  of  a  Man  22  years  old, 338 

261.  Section  of  a  Convoluted  Tubule  of  a  human  Testis, 338 

262.  Section  of  Seminiferous  Tubules  of  a  Mouse,  . 339 

263.  Spermatozoa, 341 

264.  Section  through  the  head  of  the  Epididymis  of  Man, 342 

265.  Section  of  an  adult  human  Ductulus  Efferens  Testis, 342 

266.  Section  of  a  human  Ductus  Epididymidis 343 

267.  Section  of  the  Initial  Portion  of  a  human  Ductus  Deferens, 343 

268.  Section  of  a  human  Prostate,       345 

269.  Section  of  the  Pars  Cavernosa  Urethra;  of  Man, 347 

270.  Section  of  the  Ovary  of  a  Child, 348 

271.  Section  of  the  Ovary  of  an  Infant, ,  349 

272.  Section  of  the  Cortex  of  the  Ovary  of  a  Rabbit, 349 

273.  Section  of  a  large  Vesicular  Follicle  of  a  Child,      350 

274.  An  Ovum  from  a  Vesicular  Follicle  of  a  Cow, 351 

275.  Corpus  Luteum  of  a  Rabbit ;   Corpus  Luteura  of  a  Cat, 352 

276.  Transverse  Section  of  a  human  Oviduct,           354 

277.  Section  of  the  Middle  of  the  Uterus  of  a  Girl, 355 

278.  Mucous  Membrane  of  the  Resting  Uterus  of  a  young  Woman, 356 

279.  Mucous  Membrane  of  a  Virgin  Uterus  during  the  first  day  of  Menstruation,  ....  357 

280.  Section  of  the  Mucous  Membrane  of  a  human  Uterus  one  month  Pregnant,    ....  359 

251.  Section  of  a  Uterus  about  seven  months  pregnant,  with  the  Fetal  Membranes  in  situ,  360 

252.  Decidual  Cells, 361 

283.  Section  of  a  normal  human  Placenta  of  about  seven  months,  in  situ, 363 

284.  Diagram  of  the  Human  Placenta  at  the  close  of  Pregnancy,              364 

285.  Section  of  a  small  and  a  large  Chorionic  Villus  of  a  human  Placenta  at  the  end  of 

Pregnancy, 365 

286.  Isolated  Elements  of  the  Testis  of  an  Ox, 369 

287.  Section  of  a  Human  Ovary;   Tunica  Albuginea,     ...             371 

288.  Section  of  the  Skin  of  the  Finger  of  adult  Man, 373 

289.  Epidermis  from  the  Skin  of  the  dorsum  of  the  human  Foot, 374 

290.  Section  of  the  Skin  of  the  Sole  of  the  Foot  of  adult  Man, 375 

291.  Section  of  the  Third  Phalanx  of  a  Child,  showing  a  Nail, 377 

292.  Elements  of  a  Human  Nail, 378 

293.  Section  of  a  human  Scalp,  showing  a  Hair  and  Hair-follicle, 379 

294.  Elements  of  a  human  Hair  and  Hair- Follicle, 380 

295.  Cross-Section  of  a  Hair  and  Hair-Follicle  in  the  lowerhalf  of  the  Root,       ....  381 

296.  Longitudinal  Section  of  the  Root  of  a  Hair, 382 

297.  Development:  of  a  human  Hair;   Hair-germ, 383 

298.  Development  of  a  human  Hair;   Hair-germ  and  Hair-canal, 383 

299.  Development  of  a  human  Hair;  Hair-peg, 384 

300.  Development  of  a  human  Hair;  Hair-peg, 384 

301.  Development  of  a  human  Hair;   Bulb-peg 384 

302.  Development  of  a  human  Hair;  Fiulb-peg, 385 

303.  Development  of  a  human  Hair;   Sheathed  Hair, 385 

304.  Differentiation  of  the  Sheaths  of  the  Hair-follicle,      385 

305.  Development  of  a  human  Hair  ;   Hair-canal, 386 

306.  Section  sliowing  Club-hairs, 387 

307.  Vertical  Section  of  the  Ala  Nasi  of  a  Child ;   Sebaceous  Gland, 388 

308.  Vertical  Section  of  the  Injected  Skin  of  the  Sole  of  a  human  Foot, 390 

309.  Section  of  a  human  Mammary  Gland  at  the  Period  of  Lactation, 392 

310.  Section  of  the  Mammary  Gland  of  a  Nursing  Woman, .....  393 

311.  Section  of  the  Mammary  Gland  of  a  Woman  last  Pregnant  two  years  before,     .    .    .  394 

312.  Human  Milk-Globules;    Elements  of  the  Colostrum  of  a  Pregnant  Woman,  .    .    .    .  394 

313.  Vertical  Section  of  a  human  Cornea, 400 

314.  CornealCanaliculi  and  Corneal  Spaces, 401 

315.  Corneal  Corpuscles, 401 

316.  Section  through  the  human  Sclera  and  Choroid, 402 

317-   Teased  Preparation  of  a  human  Choroid, 403 


Xvi  LIST    OF    ILLUSTRATIONS. 

FIG.  .  PAGE 

318.  Meridional  Section  through  the  Iridal  Angle  of  Man, 403 

319.  Vertical  Section  of  the  Pupillary  Portion  of  a  human  Iris 404 

320.  Vertical  Section  of  a  human  Retina, 407 

321.  Vertical  Section  of  the  Retina  of  a  Rabbit, 407 

322.  Scheme  of  the  Retina, 4^9 

323.  Isolated  Elements  of  the  Retina  of  an  Ape, 41 1 

324.  Section  of  the  Macula  and  the  Fovea  of  Man, 413 

325.  Section  of  the  Ora  Serrata  and  Pars  Ciliaris  Retinse  of  a  Man  of  thirty-seven,  .    .    .  415 

326.  Section  of  the  Optic  Entrance  of  a  human  Eye, 416 

327.  Lens-Fibers  of  an  Infant, 4^8 

328.  Capsule  and  Epithelium  of  an  adult  human  Lens, 418 

329.  Scheme  of  the  Vessels  of  the  Eye,         421 

330.  Vertical  Section  of  the  human  Cornea,  showing  Nerves, 424 

331.  Sagittal  Section  of  the  Upper  Eyelid  of  a  Child, 425 

332.  Section  of  a  human  Lacrimal  Gland, 428 

333.  Otoliths  from  the  Sacculus  of  an  Infant, 438 

334.  Section  of  the  Cochlea  of  a  Kitten, 439 

335.  Portion  of  334,  more  highly  magnified, 440 

336.  Surface  View  of  the  Lamina  Spiralis  of  a  Cat, 440 

337.  Surface  View  of  the  Lamina  Spiralis  Membranacea  of  a  Cat, 441 

338.  Lamina  Spiralis  of  a  Cat  seen  from  the  vestibular  surface, 441 

339.  Scheme  of  the  Structure  of  the  Tympanic  Wall  of  the  Cochlea, 442 

340.  From  the  Lamina  Spiralis  Membranacea  of  a  Cat, 443 

341.  Organ  of  Corti, 444 

342.  Scheme  of  the  Blood-vessels  of  the  right  human  Labyrinth,      446 

343.  Scheme  of  the  right  half  of  the  first  and  second  turns  of  the  Cochlea, 447 

344.  Section  of  the  Skin  of  the  External  Auditory  Meatus  of  an  Infant, 449 

345.  Coil-Tubule  of  an  Infant ;   Coii-Tubule  of  a  twelve-year  old  Boy, 449 

346.  Section  of  the  Mucosa  of  the  Inferior  Turbinal  of  Man, .  454 

347.  Isolated  Cells  of  the  Olfactory  Mucosa  of  a  Rabbit, 455 

348.  Nerves  of  the  Olfactory  Region  of  a  young  Rat, 45^ 

349.  Vertical  Section  of  the  Olfactory  Mucosa  of  a  Rabbit, 456 

350.  Vertical  Section  of  the  Olfactory  Mucosa  of  a  Rabbit, 457 

351.  Vertical  Section  of  two  ridges  of  the  Papilla  Foliata  of  a  Rabbit, 459 

352.  Tastebud  of  the  Papilla  Foliata  of  a  Rabbit, 459 

353.  Nerves  of  the  Taste-buds, 4^0 


PART  1. 


GENERAL  TECHNIC. 


I.  THE  LABORATORY  APPOINTMENTS. 

I.   INSTRUMENTS. 

The  Microscope. — From  my  own  experience  I  can  recommend  the 
microscopes  made  in  the  optical  works  of  Leitz  in  Wetzlar,  Seibert  in 
Wetzlar,  and  Zeiss  in  Jena,  having  repeatedly  tested  their  excellent 
workmanship.* 

It  is  not  advisable  for  the  beginner  to  purchase  a  microscope 
without  first  submitting  it  to  an  expert  for  examination.  In  order  to 
preserve  the  microscope  in  good  working  condition  it  is  necessary  to 
protect  it  from  dust ;  when  in  frequent  use  it  is  best  to  keep  it  under  a 
bell-glass,  in  a  place  not  exposed  to  sunlight.  The  tarnish  which  forms 
on  the  tube  should  be  rubbed  off  with  a  dry  piece  of  soft  filter-paper. 


*  Students  of  the  first  semester  are  advised  to  refrain  from  the  purchase  of  high-power 
oculars  and  immersion-systems.  These  should  be  bought  shortly  before  entering  upon  bacterio- 
logic  work. 

The  following  outfits  are  recommended  : 
Leitz. — Catalogue  No.  36,  1895.     Microscope  No.  4  b.      Price,  370  M.  =  $92.00.     Without 

homogeneous  immersion  and  ocular  IV,  265  M. 
Seibert. — Catalogue   No.  25,  1895.     Microscope   3    c.     Price,  449    JM.  =:=  $112.00.     Without 

homogeneous  immersion,  objective  3,  and  ocular  o,  283.50  M.  =  $71.00. 
Zeiss. — Catalogue    No.    30,    1895.     Combination  (p.    116)    7   b.     Price,    602   i1/.  =  $150.00. 

Without   homogeneous   immersion,    442    il/.  =  $110.00 ;    or   8   b.     Price,    559    M.  ^ 

$140.00.      Without  homogeneous  immersion,  399  AI.  =  $100.00. 

The  majority  of  the  work  for  this  book  was  carried  out  with  a  Leitz  microscope. 

Editor's  remark :  Of  American  microscopes,  those  made  by  the  Bausch  &  Lomb 
Optical  Co.,  Rochester,  N.  Y.,  and  New  York  City,  are  recommended. 

For  histologic  work  the  following  outfit  is  suitable  : 

Stand  BB. — Oculars,  i-inch  and  3-inch.  Objectives,  2^-inch  and  ^^-inch.  Catalogue 
1895.  Price,  $62.50.  For  cytologic  and  bacteriologic  work  a  J^-inch  oil-immersion  objective 
(price,  $44)  and  an  Abbe  condenser  and  iris-diaphragm  should  be  added.  For  convenience  a 
double  or  triple  revolver  for  the  objectives  is  desirable. 

17 


1 8  HISTOLOGY. 

Smirches  on  the  lenses*  and  on  the  mirrors  should  be  removed  with  soft 
leather,  and  if  this  does  not  answer  the  purpose, — as,  for  example,  when 
a  lens  is  smeared  with  canada-balsam, — a  small  piece  of  fine  linen 
moistened  with  a  drop  of  pure  alcohol  should  be  used.  In  the  latter 
procedure  great  care  must  be  exercised  lest  the  alcohol  penetrate  the 
setting  of  the  lenses  and  dissolve  the  balsam  with  which  they  are 
cemented  together.  Therefore  the  balsam  should  be  quickly  rubbed  oft 
with  the  moistened  linen  and  the  lens  carefully  dried.  After  using  an 
immersion  lens  the  cedar  oil  clinging  to  it  should  be  removed  by  means 
of  a  patch  of  linen  moistened  with  benzin ;  the  free  surface  of  the 
cover-glass  of  the  preparation  examined  with  the  immersion  lens  should 
be  cleaned  in  the  same  way.  The  screws  of  the  microscope  should  be 
cleaned  with  benzin. 

A  good  razor,  flat  on  one  side.  It  should  always  be  kept  sharp, 
and  before  each  use  should  be  drawn  without  pressure  over  the  strop. 
The  honing  of  it  should  be  left  to  the  instrument-maker.  The  razor 
should  be  used  only  in  the  preparation  of  microscopic  sections. 

A  fine  whetstone. 

A  pair  of  small,  straight  scissors. 

A  pair  of  easily-closing  small  forceps,  with  smooth  or  only  slightly 
grooved  points. 

Four  dissecting  needles  with  wooden  holders :  two  are  to  be  heated, 
then  slightly  bent,  heated  again  and  thrust  into  solid  paraffin,  by  which 
they  are  again  hardened.  The  other  two  must  be  kept  clean  and  sharply 
pointed  ;  for  delicate  dissections  the  needles  must  be  pointed  and  polished, 
first  on  the  whetstone  and  then  on  the  strop. 

A  flexible  section-lifter,  for  the  transfer  of  sections  from  fluids  to  the 
slide,  is  very  useful  but  not  absolutely  necessary.  A  scalpel  having  a 
broad  blade  can  be  used  instead. 

Pins,  quills,  cork  disks,  a  fine  sable  brush. 

A  crayon,  for  writing  on  glass.  (If  the  glass  is  oily  it  must  first  be 
cleansed  with  alcohol.) 

Slides,  of  clear  glass,  not  more  than  i  to  1.5  mm.  in  thickness,  with 
the  edges  ground. 

Cover-glasses,  measuring  15  to  18  mm.  in  diameter,  are  generally 
large  enough;  the  thickness  may  vary  from  o. i  to  0.2  mm.;  those 
with  a  greenish  shimmer  at  the  edges  are  preferable  to  the  pure  white 
covers,  which  blur  in  time. 

*  The  objective  lenses  must  not  be  unscrewed. 


THE    LABORATORY    APPOINTMENTS.  I9 

Small,  wide-mouthed  bottles.  One  dozen,  capacity  30  c.c.  and  over, 
with  cork  stoppers. 

Several  glass  preparation  jars  (preserve  jars),  with  tightly-fitting 
covers.      Height,  8  to  12  cm.  ;  diameter,  6  to  10  cm. 

A  cylindrical  graduate,  capacity  100  to  i  50  c.c. 

A  glass  fumiel,  upper  diameter  8  to  10  cm. 

A  pipet.  Small  pipets  may  be  prepared  by  heating  in  a  gas-flame 
a  glass  tube  i  cm.  thick  and  10  cm.  long,  pulling  one  end  to  a  point  and 
placing  on  the  other  a  small  rubber  bulb. 

A  dozen  zvatch-glasses  of  5  cm.  diameter. 

A  dozen  test-tubes,  10  cm.  long  and   12  mm.  wide. 

Glass  rods,  3  mm.  thick,  1 5  cm.  long,  some  drawn  to  a  point  at  the 
end. 

Old  bottles  that  have  been  thoroughly  cleansed  will  answer  as  recep- 
tacles for  reagents.  In  most  cases  the  bottles  can  be  cleansed  with  water, 
but  sometimes  it  is  necessary  to  rinse  them  with  crude  hydrochloric  acid 
or  with  potash  lye,  then  with  ordinary  water,  then  with  distilled  water, 
and  finally  with  alcohol. 

Glass  dishes  ("  Stender  "  dishes)  6  to  8  cm.  in  diameter,  with  ground 
covers,  are  not  absolutely  necessary,  but  very  useful.*  In  many  cases 
they  may  be  replaced  by  saucers,  food  dishes  for  birds,  etc. 

A  few  sheets  of  thin,  white  filter-paper,  large  and  small  gummed 
labels,  soft  pieces  of  linen  (old  handkerchiefs),  a  towel,  a  large  and  a 
small  bottle-brush. 

A  large  earthen  jar  for  refuse. 


2.  REAGENTS.t 
General  Rules. — Large  quantities  of  reagents  should  not  be  kept 
on  hand,  because  many  decompose  in  a  comparatively  short  time.  Cer- 
tain reagents  (see  below)  should  be  procured  or  prepared  shortly  before 
they  are  to  be  used.  Each  bottle  should  be  provided  with  a  large  label 
on  which  its  contents  are  designated  ;  it  is  advisable  to  write  on  the  label 
not  only  the  formula  of  the  reagent,  but  also  the  mode  of  its  application. 


*  Most  of  the  glassware,  including  slides  and  cover-glasses,  here  enumerated  may  be  ob- 
tained of  W.  P.  Stender,  Leipzig ;  or,  in  the  United  States,  of  the  Bausch  &  Lomb  Optical 
Co.,  New  York. 

fThe  reagents  must  be  obtained  from  a  reputable  dealer.  Excellent  dyes  and  reagents 
may  be  had  of  Dr.  Griibler,  chemical  and  physiological  laboratory,  Leipzig,  Bayer'sche  Strasse 
63.  In  the  United  States  Griibler's  stains  and  reagents  are  sold  by  Eimer  &  Amend,  New  York, 
and  others. 


20  HISTOLOGY. 

All   the  bottles  must  be  tightly  closed  with   cork  or  well-made  glass 
stoppers.     The  fluid  should  not  reach  to  the  lower  surface  of  the  cork. 

1 .  Distilled  water,  3  to  6  liters. 

2.  Normal  salt  solution,  0.75  per  cent,  (sodium  chlorid,  1.5  gm., 
distilled  water,  200  c.c). 

The  cork  must  be  provided  with  a  glass  rod  reaching  to  the  bottom 
of  the  bottle.  This  solution  spoils  easily  and  must  be  frequently  pre- 
pared afresh. 

3.  Alcohol. — {a)  Ninety-five  per  cent,  alcohol. — About  500  c.c.  should 
be  kept  on  hand.  The  alcohol  of  commerce  is  95  per  cent.,  and  in  the 
majority  of  cases  is  entirely  satisfactory  for  microscopic  purposes.  If  it 
is  desired  to  obtain  alcohol  free  from  water  (absolute  alcohol),  drop  into 
the  bottle  a  few  pieces  of  copper  sulfate  heated  until  white  (15  gm.  to 
100  c.c.  of  alcohol).  When  these  become  blue  they  must  be  replaced 
by  new  pieces  or  be  reheated.  Fresh  quicklime  serves  the  same  purpose, 
but  acts  more  slowly.* 

{b)  Ninety  per  cent,  alcohol. — Prepare  500  c.c.  by  diluting  475  c.c. 
of  95  per  cent,  alcohol  with  25  c.c.  of  distilled  water. 

{c)  Eighty  per  cent,  alcohol. — Prepare  500  c.c.  by  diluting  425  c.c. 
of  95  per  cent,  alcohol  with  75  c.c.  of  distilled  water. 

{d)  Seventy  per  cent,  alcohol. — Prepare  500  c.c.  by  mixing  370  c.c. 
of  95  per  cent,  alcohol  with  130  c.c.  of  distilled  water. 

(i)  Fifty  per  cent,  alcohol. — Prepare  500  c.c.  by  mixing  265  c.c.  of 
95  percent,  alcohol  with  235  c.c.  of  distilled  water. 

(/)  Thirty-three  per  cent,  alcohol. — (Ranvier's  one-third  alcohol). — 
This  is  prepared  by  mixing  40  c.c.  of  95  per  cent,  alcohol  with  60  c.c. 
of  distilled  water. 

4.  Acetic  acid,  50  c.c. — The  official  is  30  per  cent. 

5.  Glacial  acetic  acid. — This  should  be  procured  shortly  before  it  is 
required.      The  commercial  acid  is  96  per  cent. 

6.  Nitric  acid. — A   bottle  holding'    100   c.c.   of  concentrated  nitric 


*For  the  preparation  of  mixtures  containing  a  smaller  percentage  of  alcohol  this  equation 
will  serve : 

100  :  95  =  X  :  % 
e-g-.^ojo,  100:  95  =  x:  90 

95  X  =  90  .  100 

9000 
X  =——=94.7  or  95. 

Therefore,  to  obtain  100  c.c.  of  90  per  cent,  alcohol,  95  c.c.  of  95  per  cent,  alcohol  must 
be  mixed  with  5  c.c.  of  distilled  water.  For  our  purposes  the  errors  of  this  ratio  are  too  insig- 
nificant for  consideration. 


THE    LABORATORY    APPOINTMENTS.  21 

acid  of  1.18   sp.  gr.  (containing  32   per   cent,    of  acid  hydroxid)  should 
be  kept  in  stock. 

7.  HydrocJiloric  acid,  pure,  50  c.c. 

8.  Formal. — The  aqueous  40  per  cent,  solution  of  formaldehyde 
occurs  under  two  designations  in  commerce  :  {a)  formol  (Meister,  Lucius 
&  Briining  in  Hochst  am  Main)  ;  [b)  formalin  (Chem.  Fabrik  auf 
Aktien,  formerly  Schering,  Berlin).  For  microscopic  purposes  formalin 
is  the  less  suitable. 

9.  Chromic  acid. — A  10  per  cent,  stock  solution  should  be  prepared 
by  dissolving  lO  gm.  of  fresh  crystalline  chromic  acid  in  90  c.c.  of 
distilled  water.      From  this  prepare  : 

{ci)  A  0.1  per  cent,  chromic-acid  solution  (10  c.c.  of  stock  solution 
to  990  c.c.  of  distilled  water),  and — 

{p)  A  0.5  per  cent,  chromic-acid  solution  (50  c.c.  of  stock  solution 
to  950  c.c.  of  distilled  water). 

10.  Potassium  bichromate. — This  should  be  kept  on  hand  in  two 
solutions  : 

{a)  Thirty  gm.  to  looo  c.c.  of  distilled  water. 

{U)  Thirty-fiv^e  gm.  to  1000  c.c.  of  distilled  water  (for  Kopsch's 
fluid,  No.  12,  and  for  the  Golgi  mixture,   No.  i6). 

At  room  temperature  it  dissolves  in  from  three  to  six  days.  There- 
fore make  the  solutions  with  warm  water  or  place  the  bottles  near  the 
stove. 

11.  Potassium-bichromate-acetic  rt<:zV/ (Tellyesnickey's  fluid).  To  be 
prepared  shortly  .before  using,  by  adding  5  c.c.  of  glacial  acetic  acid  to 
100  c.c.  of  3  per  cent,  solution  of  potassium  bichromate  (No.  10  ^). 

12.  Potassium-bichromate  forjnol  (Jis.o^sch' s  ^md).  To  be  prepared 
shortly  before  using,  by  adding  20  c.c.  of  40  per  cent,  formol  (No.  8)  to 
80  c.c.  of  3.5  per  cent,  solution  of  potassium  bichromate  (No.  lo  b). 

13.  Midler's  Jluid. — Dissolve  30  gm.  of  sodium  sulfate  and  60 
gm.  of  pulverized  potassium  bichromate  in  3000  c.c.  of  distilled  water. 
The  solution  can  be  made  with  the  aid  of  heat,  like  No.   10. 

14.  M'ldler-forttwl  mixture  (Orth's  mixture).  Invariably  to  be  pre- 
pared immediately  before  using,  by  mixing  10  c.c.  of  formol  (No.  8) 
with  100  c.c.  ot   Miiller's  fluid  (No.  13). 

15.  Zenker's  flidd. — Dissolve  25  gm.  of  potassium  bichromate,  10 
gm.  of  sodium  sulfate,  and  50  gm.  of  mercuric  chlorid  in  1000  c.c.  of 
warm  distilled  water.  Before  using  add  i  c.c.  of  glacial  acetic  acid  to 
each  20  c.c.  of  the  mixture. 

16.  Golgi' s  mixture  (osmio-bichromate  mixture). — This  is  prepared 
by  pouring  together  54  c.c.  of  the   3.5  per   cent,    solution  of  potassium 


22  HISTOLOGY. 

bichromate  (lo  <^)  and  6  c.c.  of  the  2  per  cent,  osmic-acid  solution  (No. 
22).      It  should  be  prepared  shortly  before  it  is  to  be  used. 

17.  Cox-Golgi  niixtu7'e. — This  is  prepared  by  pouring  together  40 
c.c.  of  a  5  per  cent,  solution  of  potassium  bichromate,  40  c.c.  of  a  5  per 
cent,  solution  of  corrosive  sublimate,  32  c.c.  of  a  5  per  cent,  solution  of 
potassium  chromate,  and  88  c.c.  of  distilled  water.  This  mixture  may 
be  kept  in  stock. 

1 8.  Ten  per  cent,  phosphomolybdic  acid. — Fifty  c.c,  kept  in  the  dark. 

19.  Iron  solution. — Dissolve  2.5  gm.  of  ferric  alum — (NHj2Fe2- 
(SOJ^ — in  100  c.c.  of  distilled  water. 

20.  Picric  acid. — Keep  on  hand  50  gm.  of  the  crystals  and  500  c.c. 
of  a  saturated  aqueous  solution,  in  which  undissolved  crystals  in  a  stratum 
2  to  3  mm.  deep  must  always  lie  on  the  bottom  of  the  bottle.  It  dis- 
solves readily. 

21.  Chromic-acetic  acid. — To  50  c.c.  of  the  0.5  per  cent,  chromic- 
acid  solution  (9  U)  add  50  c.c.  of  distilled  water  and  from  3  to  5 
drops  of  glacial  acetic  acid. 

22.  Osmic  acid. — This  may  be  obtained  from  the  dealer — 50  c.c. 
of  a  2  per  cent,  solution — shortly  before  it  is  needed.  It  is  very 
expensive.  It  should  be  kept  in  the  dark  or  in  a  dark  glass  bottle  and 
if  well  stoppered  can  be  preserved  many  months. 

23.  Chromic-acetic-osmic  acid  (Flemming's  mixture). — Prepare  a  i 
per  cent,  chromic-acid  solution  (5  c.c.  of  the  10  per  cent,  solution  [No. 
9]  to  45  c.c.  of  distilled  water)  and  add  12  c.c.  of  2  per  cent,  osmic  acid 
and  3  c.c.  of  glacial  acetic  acid.  This  mixture  is  not  injured  by  light 
and  can  be  kept  in  stock.* 

24.  Platinum  chlorid. — Prepare  a  10  per  cent,  stock  solution,  2  gm. 
dissolved  in  20  c.c.  of  distilled  water. 

25.  Platinnm-acetic-osmic  acid  mixture  (Hermann's  mixture). — Pour 
into  60  c.c.  of  a  I  per  cent,  solution  of  platinum  chlorid  (6  c.c.  of  stock 
solution  and  54  c.c.  of  distilled  water)  8  c.c.  of  2  per  cent,  osmic-acid 
solution  and  4  c.c.  of  glacial  acetic  acid. 

26.  Saturated  subliinate  salt  solution. — Put  7.5  gm.  ot  common 
salt  into  one  liter  of  distilled  water;  after  solution  add  125  gm.  of  crys- 
talline corrosive  sublimate  and  dissolve  by  the  aid  of  heat.  Filter  the 
warm  solution.  On  cooling,  white  acicular  crystals  form  on  the  bottom 
of  the  bottle. 

27.  Silver  nitrate . — A  i  per  cent,  solution  (i  gm.  of  silver  nitrate  in 


*Tissues  fixed  in  old  Flemming's  fluid  often  stain  badly,   because  the  acetic  acid  has 
evaporated;  5  to  20  drops  of  acetic  acid  newly  added  to  the  solution  removes  this  defect. 


THE  LABORATORY  APPOINTMENTS.  23 

100  c.c.  of  distilled  water)  should  be  procured  a  short  time  before  it  is 
to  be  used.  In  a  dark  place  or  in  a  dark  bottle  it  can  be  preserved  for  a 
long  time. 

28.  Gold  cJilorid. — A  solution  of  i  gm.  of  gold  chlorid  in  100  c.c. 
of  distilled  water  should  be  procured  shortly  before  it  is  to  be  used.  It 
must  be  kept  in  the  dark  or  in  a  dark  bottle.  For  gold-chlorid  staining 
it  is  necessary  to  have  No.  29. 

29.  Fonnic  acid,  50  c.c. 

30.  Concentrated  potash  lye  (35  per  cent),  30  c.c.  The  bottle  must 
have  a  rubber  stopper  that  is  pierced  by  a  glass  rod.  It  should  be  pro- 
cured from  the  druggist. 

31.  Glycerol. — One  hundred  c.c.  of  pure  glycerol  are  to  be  kept  in 
stock  ;  also  a  solution  of  5  c.c.  of  pure  glycerol  in  25  c.c.  of  distilled 
water.  The  growth  of  fungi,  which  soon  takes  place  in  this  mixture, 
may  be  prevented  by  the  addition  of  a  small  piece  of  camphor  or  thymol. 
The  cork  of  the  bottle  should  be  provided  with  a  glass  rod. 

32.  Xylol. — On  account  of  its  sensitiveness  in  preparations  incom- 
pletely dehydrated  xylol  is  not  recommended  to  beginners. 

33.  Carbol-xylol. — Prepare  by  adding  22  gm.  of  crystalline  carbolic 
acid  to  100  c.c.  of  xylol.  This  reagent  will  clear  sections  that  are  not 
fully  dehydrated. 

34.  Xylol-balsam. — A  solution  of  canada-balsam  in  xylol.  The 
cork  of  the  bottle  should  be  provided  with  a  glass  rod. 

35.  Cover-glass  cement. — Dilute  Venetian  turpentine  with  enough 
ether  to  make  an  easily  flowing  liquid  ;  then  filter  warm  (in  a  heated 
funnel)  and  inspissate  the  filtrate  on  a  sand-bath.  The  proper  con- 
sistency is  attained  when  a  drop  transferred  with  a  glass  rod  to  a 
slide  hardens  at  once  and  becomes  so  firm  that  it  cannot  be  indented 
with  the  finger-nail.  Because  of  the  danger  of  fire,  it  is  better  to  have 
the  cement  prepared  by  the  druggist.* 

36.  HanseJi's  hematoxylin. — [ti)  Dissolve  i  gm.  of  crystallized 
hematoxylin  in  10  c.c.  of  absolute  alcohol  and  preserve  it  in  a  stoppered 
bottle.  {B)  Dissolve  20  gm.  of  potassium  alum  in  200  c.c.  of  distilled 
water,  with  the  aid  of  heat  and  when  cold  filter,  {c)  Dissolve  i  gm.  of 
potassium  permanganate  in  16  c.c.  of  distilled  water,  at  room  temper- 
ature. On  the  next  day  pour  solutions  a  and  b  into  a  porcelain  capsule, 
add  3  c.c.  of  solution  c  and,  with  constant  stirring,  heat  the  mixture 
to  boiling  and  boil  about  one  minute.      Cool  quickly  by   floating   the 


*Editor's  remark:     In  the  United  States  an  excellent  fluid  cover-glass  cement  is  pre- 
pared by  J.  D.  King,  Cottage  City,  Mass. 


24  HISTOLOGY. 

porcelain  capsule  in  cold  water.  When  cold  the  mixture  should  be 
filtered  ;  it  is  then  ready  to  use.  Cloudiness,  or  the  development  of 
fungi  in  the  mixture,  does  not  depreciate  its  effectiveness  in  the  slightest 
degree.      It  is  to  be  kept  on  hand. 

37.  DelafielcVs  hematoxylin. — {a)  Dissolve  i  gm.  ot  crystallized 
hematoxylin  in  6  c.c.  of  absolute  alcohol,  {b)  Dissolve  15  gm.  of 
ammonia  alum  in  100  c.c.  of  distilled  water,  with  the  aid  of  heat  and 
when  cold  filter.  Pour  the  two  solutions  together  and  let  the  mixture 
stand  three  days  in  a  wide-open  vessel  exposed  to  the  light ;  then  filter 
and  mix  with  25  c.c.  of  pure  glycerol  and  25  c.c.  of  methyl-alcohol. 
After  three  days  filter  the  mixture.  It  does  not  deteriorate  with  age 
and  should  be  kept  in  stock. 

38.  Weigert s  hematoxylin,  for  the  demonstration  of  the  medullated 
nerve-fibers  of  the  brain  and  the  spinal  cord.  Heat  i  gm.  of  crystallized 
hematoxylin  in  10  c.c.  of  absolute  alcohol,  plus  90  c.c.  of  distilled  water, 
and  when  cold  filter.  It  should  be  prepared  shortly  before  it  is  to  be 
used.  The  application  of  this  stain  demands  the  aid  of  the  following 
three  fluids  : 

39.  Saturated  solution  of  lithium  carbonate. — Dissolve  3  or  4 
gm.  of  lithium  carbonate  in  100  c.c.  of  distilled  water.  This  should  be 
prepared  the  day  before  using. 

40.  Solution  of  potassium  permanganate  (0.25  per  cent.). — Dissolve 
0.5  gm.  of  potassium  permanganate  in  200  c.c.  of  distilled  water.  This 
may  be  kept  on  hand. 

41.  Acid  mixture  i^dM?,  mixture). — Dissolve  i  gm.  of  pure  oxalic 
acid  and  i  gm.  of  potassium  sulfite  (K^SOg)  in  200  c.c.  of  distilled 
water.  This  mixture  should  be  prepared  one  day  before  using  and  be 
kept  in  a  well-stoppered  bottle. 

42.  Mallory's  hematoxylin. — Pour  10  c.c.  of  10  per  cent,  phospho- 
molybdic  acid  into  200  c.c.  of  distilled  water ;  in  this  dissolve  (without 
heating)  1.75  gm.  of  crystallized  hematoxylin  and  add  5  gm.  of  crystal- 
line carbolic  acid. 

43.  Neutral  carjnine  solution. — Dissolve  i  gm.  of  the  best  car- 
mine in  50  c.c.  of  cold  distilled  water  to  which  5  c.c.  of  a  solution  of 
ammonia  (liquor  ammonii  caustici)  have  been  added.  The  deep, 
cherry-red  fluid  should  stand  in  an  open  vessel  until  it  has  no  odor  of 
ammonia  Cabout  three  days)  and  then  be  filtered.  It  is  to  be  kept  in 
stock.  The  odor  of  this  solution  immediately  becomes  very  disagree- 
able, but  this  does  not  depreciate  its  staining  power. 

44.  Picrocarmine. — Pour  5  c.c.  of  solution  of  ammonia  into  50  c.c. 
of  distilled  water  and  to  this  mixture  add   i  gm.  of  the  best  carmine. 


THE    LABORATORY    APPOINTMENTS.  2$ 

Stir  with  a  glass  rod.  After  complete  solution  of  the  carmine  (in  about 
five  minutes)  add  50  c.c.  of  a  saturated  solution  of  picric  acid  and  let  the 
whole  stand  in  a  wide-open  vessel  for  two  days.  It  is  then  to  be  filtered. 
Abundant  fungous  growth  does  not  diminish  the  staining  power  of  this 
excellent  medium. 

45.  Alutn-cannine.  —  Dissolve  5  gm.  of  alum  in  100  c.c.  of  warm 
distilled  water  and  add  2  gm.  of  carmine.  Boil  this  mixture  ten  or 
twenty  minutes  and  when  cold  filter  ;  finally,  to  the  clear,  beautiful,  ruby- 
red  fluid  add  2  or  3  drops  of  liquefied  carbolic  acid. 

46.  Cannahun. — To  be  obtained  in  solution  of  Dr.  Griibler. 

47.  Borax-carmine. — Dissolve  4  gm.  of  borax  in  100  c.c.  of  warm 
distilled  water  ;  when  the  solution  has  cooled  add  3  gm.  of  the  best  car- 
mine, stirring  meanwhile,  and  then  100  c.c.  of  70  per  cent,  alcohol.  At 
the  expiration  of  twenty-four  hours  the  fluid  should  be  filtered.  It  filters 
very  slowly,  requiring  twenty-four  hours  or  more. 

Staining  with  borax-carmine  requires  after-treatment  with  70  per 
cent,  acid-alcohol,  which  is  prepared  by  adding  4  or  6  drops  of  pure 
hydrochloric  acid  to  100  c.c.  of  70  per  cent,  alcohol. 

48.  Paracarmuie. — Dissolve  4  gm.  of  carminic  acid  (Griibler),  0.5 
gm.  of  aluminum  chlorid,  and  4  gm.  of  calcium  chlorid  in  lOO  c.c.  ot 
70  per  cent,  alcohol.      This  preparation  keeps  for  a  long  time. 

49.  Sodium  carDiinate. — Dissolve  2  gm.  of  pigment  in  200  c.c. 
of  distilled  water.* 

50.  Safraiiin. — Dissolve  2  gm.  of  pigment  in  60  c.c.  of  50  per 
cent,  alcohol  (32  c.c.  of  95  per  cent,  alcohol  in  28  c.c.  of  distilled  water). 
It  is  to  be  kept  in  stock. 

51.  Eosin. — Dissolve  i  gm.  of  pigment  in  60  c.c.  of  50  per  cent, 
alcohol.      This  should  be  kept  in  stock. 

52.  Orange. — Dissolve  i  gm.  of  pigment  in  60  c.c.  of  50  percent, 
alcohol. 

53.  Congo-red. — Dissolve  i  gm.  of  pigment  in  100  c.c.  of  distilled 
water.      From  this  stock-solution  prepare — 

{a)  A  -^  per  cent,  solution  :  3  c.c.  of  stock-solution  in  100  c.c.  of 
distilled  water. 

54.  J^csnvin,  or — 


*  Editor's  remark  :  Of  the  carmine  stains,  alum- cochineal  s\iOv\6.  be  highly  recommended. 
Because  of  the  certainty  of  its  action  and  the  simplicity  of  its  application  it  is  very  useful  in 
the  hands  of  the  beginner.  It  is  prepared  by  boiling  60  gm.  of  powdered  cochineal  and  60  gm. 
of  alum  in  800  parts  of  water  for  about  twenty  minutes,  filtering  the  decoction,  and  adding  a 
small  piece  of  camphor  or  thymol  to  prevent  the  growth  of  mold.  It  can  be  kept  in  stock  for  a 
long  time. 

\ 

t 

f 


26  HISTOLOGY. 

55.  Methyl-violet  B,  may  be  kept  in  stock  in  a  saturated  aqueous 
solution  (i  gm.  in  50  c.c.  of  distilled  water). 

56.  Methylene -blue. — Dissolve  i  gm.  in  100  c.c.  of  distilled  water. 
This  solution  keeps  well,  as  does  the  following,  which  is  required  for 
after-treatment. 

57.  Ammonium  picrate. — Dissolve  3  gm.  in  100  c.c.  of  distilled 
water. 

58.  Acid fuchsin  (=  rubin  S). — Dissolve  i  gm.  of  the  pigment  in 
100  c.c.  of  distilled  water. 

59.  Van  Gieson' s  picrofuchsin. — To  10  c.c.  of  i  per  cent,  solution  of 
acid  fuchsin  (No.  58)  add  lOO  c.c.  of  saturated  aqueous  solution  of  picric 
acid  (No.  20). 

60.  Resorcin-fuchsin  after  Weigert  (modification  of  Pranter). — Dis- 
solve 0.02  gm.  of  the  dry  pigment,  to  be  obtained  of  Dr.  Griibler,  in  one 
part  by  weight  (not  volume)  of  official  nitric  acid  and  100  parts  by  weight 
of  70  per  cent,  alcohol. 

61.  Westphal's  alum-carmine  dahlia. — Dissolve  i  gm.  of  dahlia  in 
25  c.c.  of  absolute  alcohol,  add  12  c.c.  of  pure  glycerol  and  5  c.c.  of 
glacial  acetic  acid,  and  pour  into  this  mixture  25  c.c.  of  alum-carmine 
(No.  45,  p.  25).      Preserve  in  a  well-stoppered  bottle. 


II.  THE  PREPARATION  OF  MICROSCOPIC 
SPECIMENS. 

INTRODUCTION. 

Very  few  organs  of  the  animal  body  are  of  a  structure  suitable  for 
microscopic  examination  without  special  preparation.  They  must  possess 
a  certain  degree  of  transparency,  which  is  attained  either  by  separating 
the  organs  into  their  elements  or  by  cutting  them  into  thin  sections — 
that  is,  either  by  isolating  or  by  sectioning.  Further,  very  few  organs 
possess  "a  consistency  that,  without  treatment,  allows  of  the  cutting  ot 
sufficiently  thin  sections  ;  they  are  either  too  soft,  in  which  case  they 
must  be  hardened,  or  too  hard  (calcified),  in  which  case  they  must  be 
decalcified.  But  fresh  objects  can  be  neither  hardened  nor  decalcified 
without  injury  to  their  structure  ;  both  processes  must  be  preceded  by 
treatment  which  rapidly  kills  the  structural  elements  and  at  the  same 
time  preserves  their  natural  form.  This  procedure  is  called  fixation. 
Usually,  the  preparation  of  thin  sections  is  possible  only  after  fixation  and 
hardening,  followed  in  some  cases  by  decalcification,  of  the  object.  The 
sections,  too,  require  further  treatment  ;  they  may  be  forthwith  ren- 
dered transparent  by  means  of  clearing  media  (which  can  be  also  suc- 
cessfully used  in  the  examination  of  fresh  objects),  or  they  may  be 
stained  before  being  made  transparent.  The  staining  materials  are  in- 
valuable aids  in  microscopic  investigations.  They  can  be  applied  in  the 
examination  of  fresh  and  even  of  living  organs.  A  large  number  of  the 
most  important  facts  have  been  discovered  by  means  of  them.  Intro- 
duced into  the  blood-vessels,  injected,  they  enable  us  to  trace  the  branch- 
ing and  course  of  their  finest  ramifications. 

§  I.  NATURE   OF    THE   MATERIAL. 

For  the  study  of  the  structural  elements  and  the  simplest  tissues, 
amphibians  (frogs,  salamanders)  are  recommended.  The  best  is  the 
spotted  salamander,*  the  elements  of  which  are  very  large.  For  the 
study   of   organs,   mammals   should   be   chosen.       In    many   cases    our 

*  Editor's  remark:  Or  the  American  Amblysloma,  A^ednriis,  etc. 
27 


28  HISTOLOGY. 

rodents  (rabbits,  guinea-pigs,  rats,  mice),  also  young  dogs,  cats,  etc., 
are  suitable.  Still  no  opportunity  to  secure  human  organs  should  be 
neglected.  Perfectly  fresh  material  can  often  be  obtained  at  surgical 
clinics.  Material  may  also  be  had  at  autopsies,  if  not  made  too  long 
after  death  ;  with  the  exception  of  the  mucous  membrane  of  the  intes- 
tinal tract,  which  decomposes  very  quickly  after  death,  many  organs  can 
be  used. 

In  general  it  is  advisable  to  place  the  organs  while  yet  warm  in  the 
fixing  fluid.  In  order  to  accomplish  this  the  following  injunctions  must 
be  observed :  Fill  the  bottles  selected  for  the  reception  of  the  objects 
with  the  appropriate  fluid  and  provide  them  with  a  label  on  which  is 
designated  the  object,  the  fluid,  the  date,  and  in  some  cases  the  hour  ; 
then  place  the  dissecting  instruments  near  at  hand  ;  then  kill  the  animal.* 

§  2.  KILLING  AND  DISSECTING  THE  ANIMALS. 

Kill  amphibians  by  cutting  through  the  vertebral  column  of  the 
neck  with  strong  scissors  and  destroy  brain  and  spinal  cord  by  means  of 
a  needle  introduced  through  the  wound  into  the  vertebral  canal  and  the 
cranial  cavity.  Cut  the  throat  of  mammals  by  a  deep  incision  reach- 
ing as  far  back  as  the  vertebral  column,  or  pour  chloroform  on  a  cloth 
and  press  it  to  the  nose  of  the  animal. f  Small  animals,  up  to  the 
size  of  four  centimeters,  and  embryos  may  be  placed  entire  in  the  fixing 
fluid  ;  after  about  six  hours  the  thoracic  and  abdominal  cavities  should 
be  opened  by  incisions.  In  the  dissection,  if  possible,  an  assistant  should 
hold  the  extremities  of  the  animal.  Small  animals  can  be  extended  on 
cork  or  wax  plates  and  secured  by  strong  pins  thrust  through  the  feet. 
The  organs  must  be  carefully  removed.  This  is  best  done  with  scissors 
and  forceps.  Crushing  or  pressing  the  parts,  or  taking  hold  of  them  with 
the  fingers,  must  be  entirely  avoided.  Only  the  edge  of  the  object  may 
be  grasped  by  the  forceps.  Attached  foreign  matter,  mucus,  blood, 
contents  of  the  intestines,  must  not  be  scraped  off  with  the  scalpel,  but 
should  be  removed  by  slow  twirling  in  the  respective  fixing  fluids  [or 
by  gently  shaking  the  object  in  normal  salt  solution  (p.  20)  before 
placing  it  in  the  fixing  medium. — Ed.]  . 

In  the  following  methods  it  is  not  possible  to  avoid  moistening  scis- 
sors, forceps,  needles,  glass  rods,  etc.,  with   different  fluids,  for  example, 

*  To  take  parts  from  the  living  animal  is  an  entirely  needless  cruelty  ! 

^Editor's  remark :  I  prefer  to  kill  medium-sized  and  small  animals  (rabbits,  guinea- 
pigs,  cats,  mice,  etc.)  by  placing  them  under  a  sufficiently  large  bell-glass,  together  with  a  wad 
of  absorbent  cotton  saturated  with  chloroform. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  29 

with  acids.  The  instruments  should  be  cleaned  vnmediately  after  using 
by  rinsing  in  water  and  drying.  Above  all,  avoid  dipping  a  glass 
rod  which,  for  instance,  may  be  contaminated  with  an  acid  or  a  dye  into 
another  fluid.  Apart  from  the  fact  that  thereby  the  reagents  will  be 
spoiled,  the  success  of  the  preparation  is,  as  a  consequence,  often  totally 
frustrated.  Beaker-glasses,  watch-glasses,  etc.,  are  easy  to  clean  if 
attended  to  immediately  after  using  ;  but  if,  for  example,  any  staining  fluid 
is  allowed  to  evaporate  and  dry  on  them  the  cleansing  then  becomes  very 
tedious.  Therefore  the  cleansing  of  the  glasses  immediately  after  using 
should  never  be  neglected  ;  in  case  there  be  no  time  for  this,  they  at  least 
should  be  placed  in  water. 

All  vessels  used  for  isolating,  fixing,  hardening,  staining,  etc.,  must 
be  kept  closed  and  should  not  be  placed  in  the  sun. 

§  3.   ISOLATION. 

The  process  of  isolation  is  accomplished  by  teasing  either  the  fresh 
objects  or  those  previously  treated  with  dissociating  fluids,  which  render 
the  teasing  partially  or  wholly  unnecessary.  It  is  a  difficult  task  to 
make  a  well-teased  preparation.  Great  patience  and  exact  fulfilment  of 
the  following  directions  are  indispensable  :  The  needles  must  be  sharp 
and  perfectly  clean  ;  they  should  be  previously  pointed  and  polished  on 
a  moistened  whetstone.  The  minute  object,  at  the  most  4  mm.  square, 
should  be  placed  in  a  small  drop  of  the  dissociating  or  mounting 
medium  on  a  slide  and  teased  on  a  dark  background  if  it  is  colorless, 
on  a  white  surface  if  it  is  dark  or  stained.  If  the  object  is  fibrous — 
for  example,  a  bundle  of  muscle-fibers — apply  both  needles  at  one  end 
and  separate  the  fasciculus  along  its  length  into  two  ;  in  the  same  way 
divide  one  of  these  bundles  into  two,  and  so  continue  until  the  minute 
individual  fibers  are  isolated.  At  times  it  is  difficult  to  divide  the  bundle 
along  its  entire  length  ;  in  this  case  it  is  often  sufficient  to  divide  it  for 
three-fourths  of  its  length,  allowing  the  isolated  fibers  to  remain  attached 
at  the  one  end.  The  uncovered  preparation  may  be  examined  with  the 
low  power  in  order  to  ascertain  if  the  dissection  is  fine  enough.* 

The  following  isolating  fluids  are  recommended  : 

{a)  For  Epithelial  Cells. 
Ranvier's     one-third    alcohol    (p.     20)    is  an    admirable    isolating 

*  Uncovered  preparations  lying  in  a  small  amount  of  fluid  often  appear  indistinct,  exhibit 
black  borders,  etc.,  errors  which  may  be  corrected  by  the  addition  of  a  sufficiently  large  drop 
of  fluid  and  the  application  of  a  cover-glass. 


30  HISTOLOGY. 

medium.  Place  small  pieces  from  5  to  10  mm.  square  (e.  g.,  of 
the  intestinal  mucous  membrane)  in  about  10  c.c.  of  this  fluid.  After 
four  hours  (in  the  case  of  stratified  squamous  epithelium  after  ten 
to  twenty-four  hours  or  later)  take  out  the  pieces  with  the  forceps,  care- 
fully and  slowly,  and  tap  them  lightly  against  a  slide  on  which  a  drop 
of  the  same  fluid  has  been  placed.  By  this  manipulation  many  isolated 
epithelial  cells  fall  off;  occasionally  shreds  are  detached,  which  can  be 
separated  into  their  elements  by  gently  stirring  them  with  a  needle. 
Then  apply  a  cover-glass  (p.  49)  and  examine.  If  it  is  desired  to  staijt 
the  object,  carefully  transfer  the  entire  piece  from  the  alcohol  to  about  6 
c.c.  of  picrocarmine  (p.  24).  In  two  or  four  hours  place  the  object  very 
carefully  in  5  c.c.  of  distilled  water,  and  in  five  minutes  tap  it  against 
the  slide,  which  this  time  should  have  on  it  a  drop  of  diluted  glycerol 
(p.  23).     Apply  a  cover-glass.     The  preparation  can  be  preserved. 

{b)  For   Muscle-fibers  and   Glands. 

A  35  per  cent,  solution  of  potassium  hydroxid  is  suitable 
(p.  23).  Small  cubes  from  10  to  20  mm.  in  diameter  should  be 
placed  in  10  to  20  c.c.  of  this  fluid.  In  about  an  hour  the  objects 
fall  apart  into  their  elements,  which  may  then  be  lifted  out  with 
a  needle  or  a  pipet  and  examined  under  a  cover-glass  in  a  drop  of  the 
same  lye.  The  action  of  diluted  potash  lye  is  totally  different ; 
examined  in  a  drop  of  water  the  elements  are  rapidly  destroyed.  If  the 
isolation  is  not  successful,  if  instead  a  jelly-like  softening  occurs,  the 
potash  solution  is  too  old.  Therefore  a  freshly  prepared  solution  should 
always  be  used.  The  preparations,  even  when  successful,  cannot  be 
preserved.* 

A  mixture  of  potassium  chlorate  and  nitric  acid  may  be  used.  This 
is  prepared  by  throwing  into  20  c.c.  of  pure  nitric  acid  so  much  potassium 
chlorate  (about  5  gm.)  that  an  undissolved  residue  remains  on  the 
bottom  of  the  bottle.  In  from  one  to  six  hours,  occasionally  later,  the 
object  is  sufficiently  dissociated,  and  should  then  be  transferred  to  dis- 
tilled water,  in  which  it  should  stay  for  one  hour,  but  may  remain  for  a 

^Editor's  remark:  According  to  S.  H.  Gage  ("Proc.  Amer.  Soc.  Micr.,"  1889,  p.  36), 
the  action  of  the  caustic  potash  may  be  at  any  time  most  satisfactorily  checked  by  replacing  it 
with  a  60  per  cent,  solution  of  potassium  acetate,  or  by  the  addition  of  sufficient  glacial  acetic 
acid  to  neutralize  the  caustic  potash  and  form  acetate  of  potash.  After  the  action  of  the  caustic 
potash  is  checked  the  elements  may  be  preserved  indefinitely  en  tnasse  in  a  60  per  cent,  solu- 
tion of  acetate  of  potash,  or  after  being  treated  with  a  saturated  solution  of  alum,  in  40  per  cent, 
alcohol  or  glycerol.  After  the  last  treatment  the  elements  may  even  be  satisfactorily  stained 
with  hematoxylin  or  alum-carmine. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  3 1 

week  without  injury.  Then  the  object  is  placed  on  a  slide,  where,  in  a 
drop  of  diluted  glycerol  (p.  23),  it  can  be  easily  dissected.  If  the  nitric 
acid  is  well  washed  out  the  preparation  can  be  preserved  and  can  also  be 
stained  under  the  cover-glass  (p.  53).  Placing  the  unteased  objects  in 
picrocarmine  (see  a,  p.  29)  will  not  be  successful,  because  this  stain- 
ing fluid  makes  them  brittle. 

(r)  For   Gland-tubules. 

Pure  hydrochloric  acid  is  admirable.  Small  pieces  about  i  cm. 
in  diameter  should  be  placed  in  10  c.c.  of  the  acid  and  in  from 
ten  to  twenty  hours  transferred  to  about  30  c.c.  of  distilled  water, 
which  must  be  renewed  several  times  during  twenty-four  hours. 
The  isolation  is  then  easily  accomplished  by  carefully  spreading  out  the 
pieces  with  needles  in  a  drop  of  diluted  glycerol.  The  preparation 
can  be  preserved. 

§  4.   FIXATION. 

General  Rules. — (i)  For  fixation  a  large  quantity  of  the  fluid 
should  be  used,  exceeding  the  volume  of  the  object  50  to  100  times. 
(2)  The  fluid  must  always  be  clear,  and  as  soon  as  it  becomes  turbid  must 
be  replaced  by  fresh  fluid.  It  often  becomes  turbid  within  an  hour,  or 
sooner,  after  the  introduction  of  the  object.  (3)  The  objects  to  be  fixed 
should  be  as  small  as  possible  ;  in  general  they  should  not  txceed  i  or  2 
c.c.  Should  it  be  necessary  to  preserve  the  object  entire  {e.  g.,  for  sub- 
sequent orientation),  many  deep  incisions  should  be  made  in  it  from  five 
to  ten  hours  after  placing  it  in  the  fixation  medium.  The  object  should 
not  lie  on  the  bottom  of  the  receptacle,  but  should  be  suspended  within 
it  or  placed  upon  a  thin  layer  of  defatted  cotton-wool  or  glass-wool. 

I.  Ninety-five  per  cent,  alcohol  is  especially  suitable  for  fixing  glands, 
skin,  blood-vessels,  etc.  It  acts  simultaneously  as  a  hardening  medium. 
Objects  fixed  in  alcohol  can  be  sectioned  after  twenty-four  hours  ;  *  there- 
fore it  is  well  adapted  for  the  rapid  preparation  of  specimens.  Special 
attention  should  be  given  to  the  following  details  :  (i)  The  alcohol  must 
be  renewed  in  from  three  to  four  hours,  even  though  it  is  not  turbid. 
(2)  The  objects  should  not  lie  in  contact  with  the  glass,  lest  they  adhere  to 
it ;  t  th^y  should  be  either  suspended  on  a  thread  in  the  alcohol  or 
placed  on  a  little  wad  of  cotton  on  the  bottom  of  the  vessel. 

*One  should  not  too  long  delay  using  objects  fixed  in  absolute  alcohol,  for  the  elements 
gradually  deteriorate  ;  they  should  be  sectioned  in  from  three  to  eight  days.  Sections  of  objects 
that  have  lain  only  twenty-four  hours  in  absolute  alcohol  occasionally  stain  poorly. 

f  Such  areas  appear  strongly  compressed  in  the  sections. 


32  HISTOLOGY. 

Weaker  alcohol,  for  example,  90  per  cent,  alcohol,  acts  very  dif- 
ferently, it  shrivels  the  object  and  therefore  cannot  be  used  instead  of 
95  per  cent,  alcohol. 

2.  Chromic  acid  is  mainly  used  in  two  aqueous  solutions  : 

(a)  As  a  0.1  or  a  0.5  per  cent,  solution  (p.  21),  which  is  especially 
suitable  for  organs  that  contain  much  loose  connective  tissue.  This 
strong  solution  imparts  a  superior  consistence  to  connective  tissue,  but 
has  the  disadvantage  of  making  the  staining  difficult ;  it  is  also  suitable 
for  the  fixation  of  karyokinetic  figures.  The  objects  remain  in  the  chro- 
mic-acid solution  for  from  one  to  eight  days,  are  then  washed  in  running 
water  for  from  three  to  four  hours  or,  if  this  is  not  possible,  placed  for  the 
same  length  of  time  in  water  renewed  three  or  four  times,  then  trans- 
ferred to  distilled  water  for  a  few  minutes,  and  finally  hardened  in  alco- 
hol of  gradually  increased  strength  (§  5)  and  protected  from  daylight 
(p.  35,  remark  *). 

{b)  As  a  0.05  per  cent,  solution,  which  may  be  prepared  by  dilut- 
ing the  0.1  per  cent,  solution  with  an  equal  volume  of  distilled  water. 
The  application  is  the  same  as  that  of  solution  a,  except  that  the  objects 
remain  only  twenty-four  hours  in  solution  b. 

Chromic  acid  solutions  penetrate  slowly  ;  accordingly,  if  the  tissue 
is  submitted  to  the  action  of  the  medium  for  so  brief  a  period  as  twenty- 
four  hours,  (pnly  small  pieces,  5  to  10  mm.  in  diameter,  should  be  pre- 
served. 

3.  Nitric  acid  m  a  3  per  cent,  solution  (3  c.c.  of  concentrated  nitric 
acid  [p.  20]  to  97  c.c.  of  distilled  water),  like  the  strong  chromic  acid 
solution,  is  an  admirable  medium  for  organs  rich  in  connective  tissue. 
The  objects  remain  for  from  five  to  eight  hours  in  this  solution  and  with- 
out the  previous  use  of  water  are  transferred  directly  into  alcohol  of 
gradually  increased  strength  for  hardening  (§  5). 

4.  Formaldehyde,  in  from  8  to  10  per  cent,  solution  (prepared  by 
diluting  20  c.c.  of  commercial  formol  [p.  21]  with  80  c.c.  of  distilled 
water)  is  a  good  medium  for  the  fixation  of  cell  structures  ;  it  acts 
similarly  to  osmium  solutions.*  The  objects  should  remain  48  hours 
or  more  in  the  formaldehyde  solution  and  are  then  at  once  trans- 
ferred to  absolute  alcohol,  in  which  they  are  hardened  for  at  least  two 
days. 

5.  Potassiiini-bichromaie-acetic  acid  (p.  2\).- — Place  the  objects  in 
the  liquid  and  after  from  18  to  24  hours  wash  them  for  about  three  hours 
in  (if  possible  running)  water  and  then  harden  in  gradually  strengthened 

*  Cf.  also  the  substitution  of  the  osmic  acid  in  the  Golgi  mixture. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  33 

alcohols  (p.  35).  The  advantage  of  this  reagent  lies  in  its  high  power 
of  penetration  and  in  the  rapid  course  of  the  process  :  fixation  and  hard- 
ening are  completed  in  from  4  to  5  days.  This  method,  that  with  the 
exception  of  the  liver  has  yielded  me  very  good  results,  requires  more 
time  for  staining,  e.  g.,  with  Hansen's  hematoxylin  from  15  to  60  min- 
utes, with  safranin  24  hours  instead  of  5  minutes.  Bulk  staining  of 
small  pieces  is  easily  accomplished. 

6.  Potassiiini-bicJiromatc-formol  (p.  21). — Place  the  objects  in  the 
liquid  and  after  24  hours  transfer  them  to  3.5  per  cent,  solution  of  potas- 
sium bichromate  ;  in  from  3  to  6  days  wash  in  (if  possible  running)  water 
for  from  3  to  6  hours  and  harden  in  alcohols  of  ascending  degrees  of 
strength  (p.  35). 

7.  Midler'' s  fluid. — The  objects  remain  for  from  one  to  six  weeks* 
in  a  large  volume  (up  to  400  c.c.)  of  this  solution,  are  then  washed  in 
(if  possible)  running  water,  rinsed  in  distilled  water,  and,  finally,  hard- 
ened in  the  series  of  gradually  ascending  alcohols,  under  exclusion  from 
daylight  (p.  35,  remark*).  Who  does  not  follow  with  painstaking  con- 
scientiousness the  previously  specified  general  rules  for  fixation  will  secure 
imperfect  results,  for  which  even  otherwise  experienced  microscopists 
have  held  the  blameless  Miiller's  fluid  responsible. 

8.  Midler-fornwl  mixture  (p.  21). — After  4  days'  fixation  the  objects 
are  transferred  to  pure  Miiller's  fluid  (p.  21) ;  the  subsequent  treatment 
is  the  same  as  with  Miiller's  fluid. 

9.  Zenker' s  fluid. — Metal  instruments  must  be  cleansed  immediately 
after  dipping  them  into  this  fluid.  The  objects  should  remain  in  it  for 
from  10  to  24  hours,  allowing  about  60  c.c.  of  the  reagent  to  each  one- 
centimeter  cube  of  tissue,  should  be  washed  in  running  water  for  the 
same  length  of  time,  rinsed  in  distilled  water,  and  hardened  in  the  dark 
in  alcohols  of  gradually  increasing  strength  (p.  35).  For  the  removal 
of  the  sublimate  precipitates  that  occur  in  the  tissues  add  to  the  90  per 
cent,  alcohol  enough  tincture  of  iodin  to  impart  to  the  fluid  the  color  of 
port-wine.  The  objects  remain  for  from  eight  to  fourteen  days  in  this 
iodin-alcohol,  the  color  of  which  rapidly  fades  and  therefore  it  requires 
the  daily  addition  of  enough  of  the  tincture  of  iodin  to  maintain  the  tint.f 
Finally  the  objects  are  transferred  to  pure  90  per  cent,  alcohol,  which 
is  to  be  changed  two  or  three  times,  and  in  this  they  may  remain  for  a 
week  or  longer.     (See  also  pp.  51  and  52.) 

*  Objects  may  be  left  in  Miiller's  fluid  for  a  longer  period — up  to  six  months  ;  often  they 
can  then  be  sectioned  and  stained  without  the  alcohol  hardening. 

f  If  notwithstanding  the  preparations  show  sublimate  precipitates  they  may  be  removed  by 
placing  the  sections  in  iodin-alcohol  for  about  ten  minutes.     Then  rinse  them  in    pure  alcohol, 
transfer  them  to  the  staining  fluid,  etc. 
3 


34  HISTOLOGY. 

The  results  with  Zenker's  fluid  are  good  only  when  sectioning  and 
staining  are  undertaken  soon  after  completion  of  fixation  and  hardening. 
One  year  old  Zenker  preparations  stain  less  well,  even  such  as  were 
embedded  in  paraffin.  Then  often  only  hemalum  (p.  39)  still  gives  satis- 
factory staining.  For  organs  that  are  rich  in  smooth  muscle-fibers 
Zenker's  fluid  is  less  suitable  than  other  fixing  media. 

10.  Osmic  acid  solution  (p.  22). — In  using  this  reagent  care  must  be 
taken  not  to  inhale  the  vapor,  which  is  very  irritating  to  mucous  mem- 
branes. Fixation  is  accomplished  either  by  immersing  very  small  pieces,  • 
up  to  5  mm.  cubes,  in  the  acid,  which  is  usually  employed  in  a  one  per 
cent,  solution,  of  which  only  a  small  quantity — from  i  to  6  c.c. — need, 
be  used  ;  or  by  exposing  the  moist  object  to  the  vapor  of  the  osmic  acid 
solution.  For  the  latter  purpose  pour  i  c.c.  of  the  2  per  cent,  solution 
into  a  test-tube  about  5  cm.  in  length  and  add  an  equal  volume  of  dis- 
tilled water  ;  fasten  the  object  by  means  of  quills  to  the  under  surface  of 
a  cork  stopper,  with  which  the  test-tube  is  then  to  be  securely  closed. 
In  from  ten  to  sixty  minutes,  according  to  the  size  of  the  object,  it  is 
removed  from  the  cork  and  dropped  into  the  fluid  in  the  test-tube.  In 
both  cases  the  objects  remain  in  the  acid  for  twenty-four  hours,  and 
during  this  time  the  containers  must  be  tightly  closed  and  stood  in  the 
dark.  Then  the  objects  are  taken  out,  washed  for  from  one-half  to  two 
hours  in  running  water,  rinsed  in  distilled  water,  and  hardened  in  gradu- 
ally strengthened  alcohols  (§    5). 

11.  Chromic-acetic  osmic  acid  (Flemming's  solution)  (p.  22)  is  an 
excellent  medium  for  the  fixation  of  karyokinetic  figures.  Place  the 
absolutely  fresh,  still  warm  pieces,  from  3  to  5  mm.  in  diameter,  in  4  c.c. 
of  this  fluid,  in  which  they  remain  for  from  one  to  two  days,  or  even 
longer.  Then  the  pieces  should  be  washed  in  running  water  for  one 
hour,  better  longer,  rinsed  in  distilled  water  and  hardened  in  alcohols 
of  gradually  ascending  strength  (§  5).  The  effect  of  this  mixture  on 
the  nuclei  is  different  at  the  periphery  of  the  object  than  in  the  interior, 
where  the  chromatin  networks  are  more  distinct,  because  at  the  periphery 
the  osmic  acid,  which  renders  the  nuclear  sap  granular  and  the  nuclear 
reticulum  indistinct,  acts  in  its  purity. 

1 2.  Platinmn-acetic-osmic  acid  mixture  (p.  22)  is  very  suitable  for  dis- 
playing sharply  defined  cell  boundaries.  It  is  used  like  Flemming's 
solution.* 


*Solutions  of  osmic  acid  or  mixtures  containing  osmic  acid  blacken  fat  ;  if  it  is  desired 
to  preserve  osmicated  fat  the  sections  must  not  be  cleared  in  turpentine,  absolute  ether,  or  xylol, 
which  dissolve  osmicated  fat.  Use  chloroform  (or  clove  oil)  and  mount  in  a  solution  of  balsam 
in  chloroform.  Pure  osmium  solutions  (but  not  osmium-containing  mixtures)  also  blacken 
pigment. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  35 

13.  Sublimate  salt  solution. — Place  small  cubes  of  tissue,  at  the  most 
not  over  4  mm.  in  diameter,  for  from  one  to  six  hours,  according  to  bulk, 
in  20  c.c.  of  sublimate  salt  solution  (p.  22)  ;  then  transfer  directly  into 
30  c.c.  of  gradually  strengthened  alcohols  (§  5,  p.  35)  for  hardening.  To 
the  70  per  cent,  alcohol  and  upward  add  tincture  of  iodin,  as  when 
using  Zenker's  medium  (No.  9,  p.  33).  Avoid  the  use  of  metal  instru- 
ments. 

The  fluids  that  have  been  used  for  fixation  cannot  be  used  again 
and  should  be  thrown  away. 


§    5.   HARDENING. 

Except  when  absolute  alcohol  is  used,  all  the  fixing  methods  neces- 
sitate a  supplementary  process  of  hardening.  The  best  hardening  medium 
is  alcohol  in  ascending  degrees  of  strength.  Here,  too,  the  rule  is  to  use 
abundance  of  fluid  and  to  change  the  alcohol  when  it  becomes  turbid  or 
colored.*  A  stratum  of  defatted  cottonwool,  from  2  to  4  cm.  deep, 
should  cover  the  bottom  of  the  receptacles  used  for  hardening,  in  order 
to  keep  the  water  that  settles  there  from  the  immediate  vicinity  of  the 
object. 

The  exact  application  is  as  follows  :  After  the  objects  have  been 
fixed  in  one  of  the  previously  enumerated  fluids  and  washed  in  waterf 
they  are  placed,  under  exclusion  of  daylight,  for  from  two  to  six  hours, 
according  to  the  size  of  the  object,  in  50  per  cent,  alcohol,  then  trans- 
ferred for  twelve  hours  each  to  70  per  cent,  and  80  per  cent,  alcohol,  and 
at  the  expiration  of  this  time  to  90  per  cent,  alcohol,  in  which  after 
another  period  of  from  twenty -four  to  forty-eight  hours  the  hardening 
is  completed.  In  this  alcohol  the  objects  may  remain  for  months  before 
their  final  preparation.  The  90  per  cent,  alcohol  employed  for  harden- 
ing should  be  collected  and  used  for  burning  or  for  hardening  liver  for 
embedding:. 


♦Objects  fixed  in  chromic  acid  or  in  Miiller's  fluid,  if  not  subjected  to  prolonged  wash- 
ing,— and  this  must  be  avoided  because  of  incipient  decomposition, — yield  substances  to  the 
alcohol  which  with  the  simultaneous  action  of  daylight  appear  in  the  form  of  precipitates  ;  on 
the  other  hand,  if  the  object  is  kept  in  the  dark  no  precipitates  are  formed  and  though  the 
alcohol  becomes  yellow  it  remains  clear.  It  is  on  this  account  that  the  e.xclusion  of  daylight 
has  been  recommended  above  ;  it  is  sufficient  to  place  the  bottles  in  a  dark  part  of  the  room. 
Even  the  90  per  cent,  alcohol  must  be  changed  once  daily  so  long  as  it  becomes  intensely 
yellow. 

•f-An  exception  is  made  in  the  case  of  objects  that  have  been  fixed  in  3  per  cent,  nitric 
acid.  These  should  be  transferred  directly  from  the  fixing  fluid  to  the  70  per  cent,  alcohol, 
which  must  be  changed  several  times  during  the  first  day. 


36  HISTOLOGY. 

§  6.   DECALCIFICATION. 

The  objects  to  be  decalcified  must  not  be  placed  fresh  in  the  decalcify- 
ing fluid  ;  they  must  be  previously  fixed  and  hardened.  For  this  purpose 
place  small  bones  up  to  the  size  of  a  metacarp,  teeth  entire,  and  pieces 
from  3  to  6  cm.  long  sawed  from  the  larger  bones  in  300  c.c.  of  Miiller's 
fluid  for  from  two  to  four  weeks  and,  after  previous  washing,  harden  them 
in  I  50  c.c.  of  gradually  strengthened  alcohols  (§  5).  After  the  bone  has  been 
in  the  90  per  cent,  alcohol  for  three  days  or  longer  it  is  washed  for  twenty- 
four  hours  in  running  water  and  then  transferred  to  the  decalcifying  fluid — 
diluted  nitric  acid,  prepared  by  adding  from  9  to  27  c.c.  of  pure  nitric  acid  to 
300  c.c.  of  distilled  water.  Large  quantities,  at  least  300  c.c,  of  this 
fluid  should  be  used  and  changed  daily  at  first,  later  every  four  days, 
until  the  decalcification  is  completed.  The  process  is  controlled  by 
thrusting  in  a  needle  or  by  making  an  incision  with  a  scalpel,  which 
should  be  at  once  carefully  cleaned.  Decalcified  bone  is  flexible,  soft,  and 
easily  cut.  Fetal  bones,  heads  of  embryos,  etc.,  are  decalcified  in  weaker 
nitric  acid  (i  c.c.  of  pure  nitric  acid  to  90  c.c.  of  distilled  water)  or  in 
500  c.c.  of  a  saturated  aqueous  solution  of  picric  acid  (p.  22).  The 
process  of  decalcification  requires  several  weeks  for  thick  bones,  from 
three  to  twelve  days  for  fetal  and  small  bones. 

So  soon  as  the  decalcification  is  completed  the  bones  are  placed  for 
twenty-four  hours  in  5  per  cent,  solution  of  potash  alum,  then  washed 
in  running  water  for  twenty-four  hours,  and  again  hardened  in  gradually 
strengthened  alcohols  (§  5). 

It  not  infrequently  happens  to  beginners  that  they  transfer  the  bone 
to  alcohol  before  it  is  fully  decalcified,  and  then  in  the  attempt  to  section 
it  they  discover  that  it  is  not  yet  ready  for  use.  In  such  cases  the  entire 
procedure  of  decalcification  must  be  repeated.  If  the  action  of  the  de- 
calcification medium  is  too  prolonged,  it  eventually  leads  to  the  complete 
destruction  of  the  objects. 

§  7.  SECTIONING. 
The  razor  must  be  sharp,  for  success  in  sectioning  depends  upon 
the  sharpness  of  the  knife.  The  blade  must  be  moistened  with  alcohol ; 
water  is  not  suitable,  because  it  does  not  adhere  evenly  to  the  sur- 
face of  the  blade.  Therefore,  at  each  third  or  fourth  section  dip  the 
knife  into  a  shallow  glass  dish  containing  30  c.c.  of  90  per  cent,  alcohol, 
which  at  the  same  time  serves  for  the  reception  of  the  sections  that  are 
cut.      The  razor  is  to  be  held   in  a  horizontal  position,  lightly  grasped. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  3/ 

with  the  thumb  on  the  side  of  the  cutting  edge,  the  fingers  toward  the 
back  of  the  blade,  the  dorsum  of  the  hand  directed  upward.  The  object 
to  be  sectioned  must  first  have  a  smooth  surface,  which  is  made  by- 
cutting  off  a  sHce  of  the  necessary  thickness  with  a  single  movement 
of  the  razor.  From  this  surface  the  sections  may  now  be  taken  ;  they 
should  be  cut  with  a  light,  not  too  rapid  movement,  as  smooth  as  pos- 
sible, and  of  uniform  thinness.  The  knife  must  not  be  pushed,  but 
should  be  drazvn  through  the  object,  and  that  this  may  be  done  the  por- 
tion of  the  blade  adjoining  the  handle  should  be  applied  to  the  object. 
Ten  to  twenty  sections  should  be  made  ;  they  may  be  transferred  by 
means  of  a  needle  or  by  immersing  the  blade  in  the  alcohol.*  Then 
place  the  dish  on  a  black  surface  and  search  for  the  best  sections.  The 
thinnest  sections  are  not  always  the  most  useful ;  for  many  preparations 
— for  example,  for  a  preparation  through  all  the  coats  of  the  stomach — 
thick  sections  are  recommended.  For  a  general  view  large,  thick  sec- 
tions should  be  prepared ;  for  the  study  of  minute  structures,  thin 
sections  ;  for  the  latter  purpose  small  fragments  from  i  to  2  mm.  on  a 
side  are  often  satisfactory,  or  the  marginal  portions  of  thick  sections. 

If  the  object  to  be  sectioned  is  too  small  to  be  held  with  the  fingers, 
it  should  be  embedded.  The  simplest  method  consists  in  placing  the 
object  in  a  cleft  in  a  piece  of  hardened  liver. 

Ox-liver  or,  better,  human  lardaceous  or  amyloid  liver  may  be 
used.  The  latter  may  be  obtained  from  the  pathologic  laboratories. 
Dog's  liver,  to  be  obtained  from  the  physiologic  laboratory,  is  also 
recommended.  The  liver  should  be  cut  into  pieces  about  3  cm.  high, 
2  cm.  broad,  and  2  cm.  thick,  and  these  hardened  in  90  per  cent,  alcohol, 
which  must  be  changed  within  twenty-four  hours  ;  in  three  to  five  days 
the  liver  attains  the  necessary  hardness.  The  embedding  is  then  accom- 
plished by  making  an  incision  in  one  of  these  pieces  from  the  top  half-way 
down  and  inserting  the  object  into  this  cleft.  If  the  object  is  too  thick, 
furrows  can  be  cut  in  the  liver  with  a  small  scalpel  and  the  object  fitted 
into  these.  The  object  requires  no  further  staying  except,  perhaps,  bind- 
ing with  a  silk  thread. 

As  a  rule  I  embed  objects  in  liver ;  very  thin  sections  can  be 
made  so  soon  as  one  has  a  certain  amount  of  .skill  and  this  can  be  easily 
acquired  in  the  course  of  a  few  weeks. 

§  8.    STAINING. 
Before  using  a  stain   it  should  always  be  filtered.     A  small  funnel 

*Very  thin  sections  that  are  not  to  be  stained  or  that  have  been  stained  in  bulk  may  be 
transferred  directly  to  the  slide  by  inclining  the  blade  and  slipping  or  rinsing  them  ofif. 


38  HISTOLOGY. 

can  be  made  by  simply  twice  folding  a  piece  of  filter-paper  5  cm.  in 
diameter  and  supporting  it  in  a  cork  frame,  which  can  be  made  by  cutting 
out  a  piece  2  cm.  square  from  a  cork  plate  5  cm.  square.  The  frame  is 
then  mounted  on  four  long  pins.  Such  a  funnel  and  frame  can  be  used 
repeatedly,  but  only  for  the  same  fluid.  The  sections  should  not  float 
on  the  surface  of  the  staining  fluid ;  they  must  be  submerged  with 
needles. 

I.  Nuclear  staining  with  Hansen's  hematoxylin  (p.  23). — Filter  from 
3  to  4  c.c.  of  the  staining  fluid  into  a  watch-glass  and  in  it  place  the  sec- 
tions. The  time  in  which  the  sections  stain  varies  greatly.  Sections 
fixed  and  hardened  in  alcohol  stain  in  from  one  to  three  minutes.  If 
Miiller's  flxuid  or  potassium-bichromate-acetic  acid  was  used  for  fixing, 
the  sections  must  remain  in  the  staining  fluid  somewhat  longer,  up  to  five 
minutes  and  more.* 

From  the  stain  the  sections  are  transferred  to  a  watch-glass  contain- 
ing distilled  water,  in  which  they  are  washed, — i.  e.,  gently  moved  about 
with  the  needle  to  remove  the  excess  of  dye, — and  then  placed  in  a  glass 
containing  30  c.c.  of  distilled  water.  In  this  the  sections  must  remain  at 
least  five  minutes,  during  which  their  blue-red  color  gradually  changes 
to  a  beautiful  deep  blue,  which  becomes  the  purer  the  longer  (up  to 
twenty-four  hours)  the  sections  are  allowed  to  remain  in  the  water. 
When  a  preparation  is  overstained  the  hematoxylin  can  be  partially  ex- 
tracted by  placing  the  sections  in  a  watch-glass  containing  5  c.c.  of  dis- 
tilled water  to  which  2  or  3  drops  of  acetic  acid  have  been  added.  In 
about  5  minutes  the  sections  become  lighter  and  are  then  transferred  to 
distilled  water,  which  must  be  changed  several  times,  by  means  of  which 
the  color,  made  red  by  the  acetic  acid,  becomes  blue  again.  At  first  the 
sections  have  a  faded  blue  tint ;  usually  the  differentiation  occurs  in 
about  five  minutes,  but  sometimes  not  for  hours.  When  it  is  complete 
certain  details  can  be  recognized  even  by  the  unaided  eye. 

Beginners  are  recommended  to  leave  the  sections  for  different  lengths 
of  time — one,  three,  or  five  minutes — in  the  stain,  in  order  to  learn  the 
time    required   to   produce   successful    staining.      The    chief  essential  in 


*  Sections  fixed  in  the  strong  solution  of  chromic  acid  or  in  Zenker's  fluid,  or  objects  not 
entirely  free  from  acid,  often  stain  very  slowly,  occasionally  not  at  all.  This  defect  can  be 
remedied  either  by  keeping  the  objects  from  two  to  three  months  in  90  per  cent,  alcohol,  which 
must  be  changed  two  or  three  times  during  this  period,  or  by  treating  the  sections  for  from  five 
to  ten  minutes  with  5  c.c.  of  distilled  water  to  which  from  3  to  7  drops  of  35  per  cent,  solution 
of  potassium  hydroxid  have  been  added.  The  sections  are  then  to  be  transferred  for  from  one  to 
two  minutes  to  a  watch-glass  containing  pure  distilled  water  and  from  this  into  the  hematoxy- 
lin.    In  from  five  to  ten  minutes  such  sections  will  also  stain. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  39 

hematoxylin  staining  is  thorough  tvashuig  ;  if  the  water  becomes  blue,  it 

must   be    replaced  by  fresh.      The    used   stain   should  be  poured  back 

through  the  filter  into  the  hematoxylin  bottle.     The  watch-glass  should 

be  immediately  cleaned. 

Instead  of  Hansen's  hematoxylin  P.  Mayer's  hemaliwi  (haemalum  pur., 
Griibler)  may  be  used.  It  is  prepared  by  dissolving  with  the  aid  of  lieat 
0.5  gui.  of  hemalum  in  25  c.c.  of  90  per  cent,  alcohol  and  mixing  this  with  a 
solution  of  25  gm.  of  alum  in  500  c.c.  of  distilled  water.  The  application 
is  the  same  as  for  Hansen's  hematoxylin.  It  can  also  be  used  for  bulk  stain- 
ing, allowing  24  hours  for  penetration.  Large  objects  stained  in  bulk  must  be 
washed  out  with  a  i  per  cent,  solution  of  alum. 

2.  Nuclear  staining  zuith  aluni-carniinc  (p.  25)  or  zvith  carina  hem 
(p.  25). — Filter  from  3  to  4  c.c.  of  the  staining  fluid  into  a  watch-glass, 
place  the  sections  in  it,  and  allow  them  to  stain  for  at  least  five  minutes. 
The  advantage  of  alum-carmine  lies  in  this,  that  the  sections  may  be  left 
in  it  for  a  longer  period  without  becoming  overstained,  which  is  more 
apt  to  occur  with  hematoxylin  ;  a  disadvantage  is  that  alum-carmine  is  a 
pure  nuclear  stain,  while  in  hematoxylin  staining  the  protoplasm  too  ac- 
quires color,  a  gray  or  gray-violet  tone,  and  is  thereby  more  easily 
recognized. 

3.  Disuse  staining. — For  staining  the  protoplasm  and  the  inter- 
cellular substance.  » 

{a)  SI oiv  staining. — A  small  drop  of  neutral  carmine  solution  (p.  24)  is 
transferred  by  means  of  a  glass  rod  to  a  capsule  containing  20  c.c.  of  dis- 
tilled water,  on  the  bottom  of  which  lies  a  small  piece  of  filter-paper.* 
The  sections  remain  overnight  in  this  fluid.  The  paler  the  rose  color  of 
the  fluid  the  longer  the  time  required  for  staining  and  the  more  beautiful 
the  result  will  be.  The  beginner  is  always  inclined  to  regard  the  pale- 
rose  fluid  as  too  dilute  to  secure  good  staining,  until  on  the  following 
day  the  deep  pink  to  red  sections  teach  him  better. 

This  stain  can  be  used  alone  only  in  a  few  cases,  but  is  highly 
recommended  for  double-staining.  The  sections  should  be  stained  first 
with  the  carmine  solution,  then  with  hematoxylin. 

Staining  with  orange  for  from  12  to  24  hours  (10  c.c.  of  95  per 
cent,  alcohol  to  which  from  2  to  4  drops  of  solution  of  orange  (p.  25) 
have  been  added)  yields  effective  pictures.  Stain  first  with  hematoxylin, 
then  with  orange  or  with  eosin  (2  to  4  drops  of  eosin  (p.  25)  in  10  c.c.  of 
distilled  water). 

{b)  Rapid  staining. — Add  10  drops  of  a  solution  of  eosin  (p.  25) 
to  3  or  4  c.c.  of  distilled  water.      In  this  the  sections  remain  for  from  one 

*  If  the  filter-paper  is  omitted  the  sections  stain  only  on  the  one  side. 


40  HISTOLOGY. 

to  five  minutes,  are  then  washed  in  distilled  water,  and  then  placed  in 
30  c.c.  of  fresh  distilled  water  (see  No.  i,  p.  38).  The  stain  may  be 
used  alone  or  combined  with  hematoxylin  ;  in  the  latter  case  the  whole 
procedure  of  hematoxylin  staining  is  to  be  carried  out  first,  then  that  of 
eosin  staining. 

4.  Staining  of  the  chromatin  substance. — For  nuclear  division. 
Place  the  objects  for  from  five  to  ten  minutes  in  a  watch-glass  containing 
10  c.c.  of  distilled  water  and  one  drop  of  pure  hydrochloric  acid  ;  wash 
them  for  one  minute  in  distilled  water  and  transfer  them  to  a  watch- 
glassful  of  safranin  solution  (p.  25),  in  which  they  should  remain  five  min- 
utes. The  sections  or  membranes  are  then  lifted  out  with  the  needle  and 
placed  in  about  5  c.c.  of  absolute  alcohol  for  decolorization.  When  the 
sections  no  longer  give  off  much  of  the  dye  (usually  in  from  one  to  two 
minutes),  they  are  transferred  to  5  c.c,  of  fresh  absolute  alcohol  for  one 
minute,  then  cleared  and  mounted  (§  10,  3,  p.  50).  If  the  immersion  in 
absolute  alcohol  is  too  prolonged,  it  may  lead  to  total  decolorization  of 
the  preparation.  Failure  in  staining  is  usually  due  to  an  insufficient 
amount  of  acetic  acid  in  the  Flemming's  solution  (p.  22,  remark). 

5.  Staining  in  bulk* — Nuclear  staining  of  the  entire  object  before 
sectioning  : 

(a)  Borax-carmine. — The  fixed  and  hardened  objects  are  placed  in 
30  c.c.  of  borax-carmine  for  twenty-four  hours  if  they  are  small  (5  mm. 
square),  for  from  two  to  three  days  if  they  are  large.  From  this  they 
are  transferred  directly  to  25  c.c.  of  acid-alcohol  (p.  25) ;  the  used  borax- 
carmine  may  be  returned  to  the  bottle.  In  a  few  minutes  the  acid-al- 
cohol acquires  a  red  color  f  and  must  be  replaced  by  fresh,  which  should 
be  again  renewed  in  about  fifteen  minutes  ;  this  renewal  must  be  repeated 
until  the  alcohol  no  longer  becomes  red.  %  The  object  is  then  trans- 
ferred to  90  per  cent,  alcohol,  and  if  after  twenty-four  hours  it  is  not 
sufficiently  hardened  to  be  sectioned,  it  is  placed  for  twenty-four  hours 
or  longer  in  95  per  cent,  alcohol. 


*  Editor'' s  remark :  It  is  especially  for  staining  in  bulk  that  ahim- cochineal  (recom- 
mended on  p.  25,  remark)  proves  very  useful.  It  has  the  advantage  of  not  overstaining,  and 
does  not  need  in  its  application  a  special  discharging  fluid.  Stain  the  pieces  for  about  twenty- 
four  hours  and  vi^ash  them  in  several  changes  of  water  to  remove  the  excess  of  stain  and  the 
alum  ;   then  transfer  to  alcohols  of  gradually  increased  strength. 

f  Preparations  fixed  in  Miiller's  fluid  often  give  off  very  little  dye. 

I  This  may  require  from  one  to  three  days ;  during  the  first  day  the  fluid  should  be 
changed  every  two  hours,  subsequently  every  four  hours.  If  you  wish  to  be  economical  take  a 
needle  and  gently  push  the  object  out  of  the  area  of  red  fluid  in  which  it  lies  into  an  uncolored 
portion  of  the  alcoh  il. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  4 1 

{b)  Paracarminc. — This  stain  (p.  25)  penetrates  easily  and  in  this 
respect  is  preferable  to  borax-carmine  ;  pieces  from  2  to  3  cm.  on  a  side 
can  be  stained  in  bulk  in  24  hours.  The  pieces  are  transferred  from  the 
paracarmine  to  70  per  cent,  (not  acid)  alcohol,  that  when  colored  is  to 
be  changed  for  fresh  ;  follow  by  90  and  95  per  cent,  alcohol.  This  re- 
agent stains  not  only  nuclei,  but  also  in  light  tone  the  protoplasm. 
Overstaining  can  be  corrected  by  placing  the  pieces  (or  sections)  in  40  c.c. 
of  70  per  cent,  alcohol  plus  i  c.c.  of  glacial  acetic  acid.  Then  treat  for 
12  hours  with  90  per  cent,  alcohol  and  from  this  transfer  to  95  per  cent, 
alcohol. 

6.  Picrocarmine . — Double-staining  :  nuclei  and  connective  tissue  red, 
protoplasm  yellow. 

Filter  about  5  c.c.  of  the  staining  fluid  (p.  24)  into  a  watch-glass.  The 
length  of  time  in  which  picrocarmine  acts  differs  greatly  for  individual 
objects  and  can  be  approximately  given  only  in  the  special  directions. 
When  the  staining  is  completed  the  dye  is  filtered  back  into  the  bottle 
and  the  object  transferred  for  from  ten  to  thirty  minutes  to  10  c.c. 
of  distilled  water.  (The  latter  procedure  is  omitted  in  staining  under 
the  cover-glass,  p.  53.)  If  the  object,  e.  g.,  2.  section,  is  to  be  dehy- 
drated in  absolute  alcohol  (p.  50),  it  must  not  be  allowed  to  remain  in 
this  reagent  longer  than  from  one  to  two  minutes,  because  the  alcohol 
extracts  the  yellow  stain  ;  or  the  decolorization  can  be  prevented  by 
adding  a  small  crystal  of  picric  acid  to  the  absolute  alcohol. 

Picrocarmine  is  preferably  used  in  the  examination  of  fresh  objects. 
If  the  solution  is  good  a  very  pretty  stain  is  obtained,  that  is  improved 
by  subsequent  treatment  with  acidulated  ghcerol,  which  renders  it  crisp 
and  clear. 

7.  Nuclear  staining  zvith  anilin  dyes. — For  this  purpose  the  best 
anilin  dyes  are  vesiivin  (p.  25)  and  methyl-violet  B  (p.  26).  Filter  5  c.c.  of 
the  staining  fluid  into  a  watch-glass  ;  in  this  place  the  sections,  which  ac- 
quire a  very  dark  color  in  from  two  to  five  minutes  ;  they  are  then  washed 
in  distilled  water  and  transferred  to  a  watch-glass  containing  absolute 
alcohol,  in  which  they  give  off  the  dye  abundantly.  In  a  few  minutes, 
from  three  to  five,  the  sections  become  paler,  and  individual  parts 
{e.  g.,  the  glands  of  the  skin)  can  be  detected  by  the  unaided  eye.  The 
sections  are  now  to  be  transferred  to  another  watch-glass  containing 
5  c.c.  of  absolute  alcohol,  and  in  about  two  minutes  they  may  be 
cleared  and  mounted  in  balsam.  The  result  is  a  very  beautiful  per- 
manent nuclear  stain.  A  disadvantage  lies  in  the  necessity  for  using  so 
much  absolute  alcohol. 

8.  Saf ratlin  (p.  25)  can  be  similarly  employed.     The  sections  stained 


42  HISTOLOGY. 

for  five  minutes  are  washed  for  thirty  seconds  in  a  watch-glass  containing 
95  per  cent,  alcohol  and  then  transferred  to  absolute  alcohol,  which  must 
be  replaced  by  fresh  so  soon  as  it  becomes  intensely  red.  In  from  five 
to  fifteen  minutes — the  time  varies  according  to  the  thickness  of  the  sec- 
tions— they  are  sufficiently  decolorized  and  are  then  to  be  cleared  and 
mounted  in  xylol-balsam  (p.  50). 

9.  Methylene-blue  for  staining  axis-cylinders. — This  method  is  appli- 
cable only  to  perfectly  fresh,  "overliving"  preparations.  Prepare  a  one- 
fifteenth  per  cent,  solution,  by  adding  i  c.c.  of  a  i  per  cent,  solution 
(p.  26)  to  I  5  c.c.  of  distilled  water.  The  fresh  preparation  is  treated  on 
the  slide  with  a  few  drops  of  this  diluted  staining  fluid  and  meanwhile 
covered  with  a  watch-glass,  to  prevent  evaporation,  but  not  so  as  to  make 
an  hermetic  cover,  since  the  access  of  atmospheric  air  is  necessary  to  the 
success  of  the  staining.  The  reaction  occurs  in  from  one  to  one  and  a 
half  hours  ;  it  can  be  rendered  more  certain  by  gently  moving  the  prep- 
aration to  and  fro  and  by  placing  it  in  an  oven  at  36.5°  to  37.7°  C. 
In  order  to  prevent  the  drying  of  the  preparation  during  this  period  a 
drop  of  the  diluted  staining  fluid  or  of  normal  salt  solution  should  be 
added  from  time  to  time.  Then  cover  with  a  cover-glass.  The  result 
is  a  beautiful  blue  coloration  of  the  axis-cylinders.  Other  elements  often 
are  stained,  the  nuclei,  connective -tissue  fibers,  etc.,  and  with  more  pro- 
longed action  of  the  reagent  also  the  medullary  sheaths  of  the  nerves. 
The  preparation  may  be  preserved  as  follows  :  replace  the  staining  fluid 
with  a  drop  of  ammonium  picrate  solution  (p.  26)  according  to  the 
method  given  on  page  53  ;  this  converts  the  blue  color  to  violet;  then 
place  a  drop  of  glycerol  at  the  edge  of  the  cover-glass,  and  it  will  grad- 
ually take  the  place  of  the  evaporating  water  of  the  ammonia  solution. 
After  eighteen  to  twenty  hours  add  another  drop  of  glycerol  and  secure 
the  cover-glass  with  cement  (p.  49).  In  the  course  of  24  hours  the 
preparations  become  thoroughly  transparent  and  not  until  then  do  they 
admit  of  close  investigation.  They  must  not  be  exposed  to  sunlight,  in 
which  they  fade  ;  in  any  case  they  soon  lose  their  original  beauty  (see 
further  Leontowitsch,  on  "The  Innervation  of  the  Human  Skin."  In- 
ternat.  Monatsschr.,  Bd.  18,  1901). 

10.  Miicus- staining  with  Delafield' s  hematoxylin. — Filter  three 
drops  of  this  stain  (p.  24)  into  a  watch-glass  containing  25  c.c.  of  dis- 
tilled water.  In  this  dilute  solution  the  sections  (preferably  of  objects 
fixed  in  Flemming's  mixture*)  are  placed  and  remain  for  two  or  three 


*  Preparations  that  have  been  fjxed  in  Miiller's  and  in  Zenker's  fluid  are  also  suitable  for 
mucus-staining. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  43 

hours.  Usually  at  the  end  of  this  period  the  mucus  {(.".£:.,  in  the  goblet- 
cells)  is  stained  an  intense  blue,  which  can  be  ascertained  by  examining 
with  low  magnification  the  sections  as  they  lie  in  the  solution.  It  is  often 
necessary  for  the  sections  to  remain  in  the  solution  for  a  longer  time. 
Then  they  are  washed  for  one  minute  and  mounted  in  balsam,  according 
to  the  rules  given  in  §  10,  3,  p.  50.  The  nuclei  also  stain  blue.  Very 
pretty  pictures  are  obtained  by  a  combination  with  safranin  and  picric 
acid,  as  in  No.  1 1. 

11.  Triple-stai)iiiig  is  accomplished  in  the  following  manner:  The 
sections  stained  in  Delafield's  hematoxylin  are  placed  for  five  minutes  in 
safranin  (p.  25)  and  then  transferred  to  5  c.c.  of  absolute  alcohol,  which 
must  be  changed  twice  within  fifteen  minutes.  The  sections  are  next 
placed  for  one  minute  in  5  c.c.  of  absolute  alcohol  to  which  five  drops 
of  a  saturated  alcoholic  solution  of  picric  acid  have  been  added  (i  gm.  of 
picric  acid  to  15  c.c.  of  absolute  alcohol),  washed  for  thirty  seconds  in 
pure  absolute  alcohol,  and  mounted  in  balsam  (p.  50). 

Result :    mucus  blue  ;  nuclei  red  ;    protoplasm  and   fibers  yellow. 

12.  I'^an  Giesoii  s  staining. — Treat  sections  with  Hansen's  hematox- 
ylin (p.  38)  for  30  minutes.      Place  the  overstained  sections  in  : 

(a)  5  c.c.  picrofuchsin  (p.  26),  1-3  minutes, 

(b)  5  c.c.  distilled  water,  10—30  seconds, 

(c)  5  c.c.  90  per  cent,  alcohol,  i  minute, 

(d)  5  c.c.  absolute  alcohol,  2  minutes, 

(e)  5  c.c.  xylol,  and  when  thoroughly  cleared, 

(f)  xylol-balsam. 

Result :  connective  tissue  shining  red,  elastic  tissue  and  muscle- 
fibers  yellow,  epithelium  and  nuclei  brown. 

This  method  should  be  applied  to  thin  sections  only  and  succeeds 
best  after  alcohol,  sublimate,  or  nitric  acid  fixation,  less  well  after  fixation 
with  solutions  of  chromic  acid  or  its  salts.  The  duration  of  the  stain  is 
brief.  This  latter  disadvantage  can  be  overcome  by  acidulation  (placing 
the  sections  previously  to  (a)  and  subsequently  to  (b)  for  i  minute  in  5 
c.c.  of  acid  alcohol,  see  No.  5,  p.  40). 

13.  Staining  of  clastic  fibers. — Sections  that  have  been  fixed  in  any 
medium  (preferably  in  alcohol)  are  placed  in  5  c.c.  of  resorcin-fuchsin 
(p.  26)  for  from  8  to  24  hours,  then  transferred  to  absolute  alcohol,  that 
after  one  minute  is  to  be  renewed.  In  from  2  to  5  minutes  the  sections 
are  cleared  in  xylol  (not  carbol-xylol)  and  mounted  in  balsam.  These 
preparations,  in  which  success  is  very  easily  attained,  exhibit  even  the 
finest  elastic  fibers  dark  blue  on  a  light  ground.  Sections  can  be  fore- 
stained  for  20  minutes  in  borax-carmine  (p.  40),  dried  with  filter-paper  (p. 


44  HISTOLOGY. 

50,  remark  §),  and  placed  directly  in  resorcin-fuchsin.  The  free  acid  of 
the  latter  provides  for  the  differentiation.  Eventually  orange  (p.  39,  3) 
may  be  applied  as  a  ground  stain. 

14.  Staining  of  connective- tissue  fibrils. — By  means  of  glass  rods 
place  thin  sections  of  objects  fixed  in  any  medium  (preferably  in  alcohol) 
in  5  c.c.  of  10  per  cent,  phosphomolybdic  acid,  and  after  from  one  to  ten 
minutes  wash  for  a  couple  of  seconds  in  distilled  water  ;  stain  for  from  five 
to  twenty  minutes  in  5  c.c.  of  Mallory's  hematoxylin  (p.  24),  rinse  well  in 
distilled  water  and  place  in  10  c.c.  of  50  per  cent,  alcohol ;  after  another 
five  minutes  dehydrate  in  absolute  alcohol,  clear  in  xylol,  and  mount  in 
xylol-balsam  (see  §  10,  3,  p.  50).  The  connective  tissue  stains  intensely 
blue.  If  it  is  desired  to  stain  nuclei,  the  sections  must  be  forestained 
with  safranin  (p.  40,  4),  or  with  borax-carmine  (p.  40,  5).  Everywhere, 
in  glands,  mucous  membranes,  the  skin,  etc.,  I  have  obtained  very 
instructive  pictures. 

I  5 .  M.  Heidenhain' s  iron-hematoxylin. — For  staining  centrosomes,  se- 
cretory capillaries,  cement  bars,  and  gland  granules.  Fix  the  object  pref- 
erably in  sublimate  (p.  35),  in  Zenker's  medium  (p.  33),  or  in  Flemming's 
mixture  (p.  34),  for  granules  in  potassium-bichromate-formol  (p.  33)  ; 
embed  in  paraffin,  cut  on  the  microtome,  and  fasten  the  sections  (which 
should  be  very  thin)  to  the  slide  (see  Microtome  Technic).  Transfer  the 
slide  with  the  sections  from  the  absolute  alcohol  to  a  capsule  containing 
50  c.c.  of  the  iron  solution  (p.  22)  ;  after  from  six  to  twelve  hours  re- 
move from  the  mordant,  rinse  for  a  couple  of  seconds  in  distilled  water, 
and  place  for  from  twelve  to  thirty-six  hours  in  a  mixture  of  30  c.c.  of 
Weigert's  hematoxylin  (p.  24)  and  30  c.c.  of  distilled  water.*  The  sec- 
tions, which  have  become  black  and  wholly  untransparent,  are  now  rinsed 
in  tap-water  and  then  returned  into  the  iron  solution  for  bleaching  and 
differentiation.  When  this  is  accomplished  wash  them  for  about  fifteen 
minutes  (not  more)  in  running  water, — common  water  is  indispensable, — 
stain  with  picrofuchsin  (cf.  No.  12,  p.  43),  and  after  the  customary  pre- 
liminary treatment  mount  in  xylol  balsam  (p.  50).  When  the  decolora- 
tion is  slowly  and  carefully  done  this  admirable  method  easily  succeeds, 
but  the  exact  duration  of  this  process  cannot  be  given  ;  the  slide  must 
be  frequently  removed  from  the  iron  solution,  washed  with  tap-water,  and 
examined  with  a  high-power  objective,  to  ascertain  if  the  differentiation 
is  completed. 


*  This  diluted  hematoxylin  can  be  repeatedly  used  and  should  be  saved.     Old  Weigert's 
hematoxylin  is  preferable  to  the  freshly  prepared  stain. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMEN'S.  45 

16.  Silver  Staining. — For  the  exhibition  of  cell  boundaries  and  the 
staining  of  cement-substance.* 

The  use  of  metallic  instruments  must  be  avoided  ;  glass  rods  should 
be  employed  and  quills  instead  of  pins. 

The  object  is  immersed  for  from  one-half  to  ten  minutes,  according  to 
its  thickness,  in  from  10  to  20  c.c.  of  a  i  per  cent,  or  weaker  (see  Special 
Technic)  solution  of  silver  nitrate  (p.  22),  which  meanwhile  becomes 
milky  and  turbid  ;  it  is  then  removed  with  glass  rods,  washed,  placed  in 
a  porcelain  capsule  containing  100  c.c.  of  distilled  water,  and  exposed  to 
direct  sunlight.  In  a  few  minutes  a  faint  brown  coloration  appears,  the 
sign  of  a  successful  reduction.  So  soon  as  the  object  has  become  a 
deep  red-brown  (usually  in  from  five  to  ten  minutes)  it  is  taken  out, 
placed  in  a  watch-glass  containing  distilled  water  to  which  a  few  grains 
of  common  salt  have  been  added,  and  at  the  end  of  five  or  ten  minutes 
transferred  to  30  c.c.  of  70  per  cent,  alcohol  and  stood  in  the  dark  ;  in 
from  three  to  ten  hours  the  70  per  cent,  should  be  replaced  by  90  per 
cent,  alcohol.  The  immersion  in  the  silver  solution  must  be  done 
under  exclusion  of  sunlight ;  the  reduction,  on  the  other  hand,  must  be 
undertaken  only  in  sunlight.f  If  the  sun  does  not  shine  the  object,  after 
treatment  with  the  silver  solution  and  washing  in  distilled  water,  is  to  be 
preserved  in  the  dark  in  30  c.c.  of  70  per  cent,  (later  90  per  cent.)  alco- 
hol, and  in  this  exposed  to  sunlight  at  the  earliest  opportunity. 

17.  GolgV s  "  black  "  reaction. — For  demonstration  of  the  elements 
of  the  nervous  system  and  the  secretory  passages.  J 

This  method  unites  fixing  and  staining.  The  objects  must  be  as 
fresh  as  possible  and  in  general  their  diameter  should  not  exceed  4  mm. 
It  is  not  easy  to  cut  fresh  brain  or  other  organs  into  pieces  of  this  size  with- 
out bruising  the  delicate  tissue  ;   therefore  place  larger  pieces  (up  to  2 


*  The  cross-striations  that  appear  in  different  tissues  and  organs  when  treated  with  silver 
nitrate,  particularly  in  nerve-fibers,  blood-vessels,  cartilages,  etc.,  are  artifacts  ;  they  appear 
where  colloid  structures  coagulate  under  the  action  of  silver  nitrate,  especially  when  under  the 
simultaneous  influence  of  an  acid. 

t  The  reduction  takes  place  in  ordinary  daylight,  but  slowly,  and  yields  less  satisfactory 
results. 

X  Editor'' s  remai'k  :  In  American  laboratories  a  modification  of  Golgi's  method  by  Cox  is 
often  used  with  excellent  results.  This  modification  is  particularly  recommended  to  beginners, 
because  it  is  very  simple  and  nearly  always  successful.  In  its  application  the  following  direc- 
tions should  be  observed  :  Put  small  cubes,  2  cm.  or  less,  of  the  organs  of  the  central  nervous 
system  of  adult  or  newborn  animals  of  from  six  to  ten  weeks  in  the  Cox-Goigi  mixture,  the 
formula  of  which  is  given  on  page  22  (No.  17),  using  10  to  20  times  the  volume  of  the  object 
treated.  Change  the  fluid  at  the  following  intervals  :  after  twenty-four  hours  ;  three  days  ;  eight 
days  ;  fifteen  days;   twenty-one  days  ;   thirty  days.      The   objects  should   remain  in  the  mixture 


46  HISTOLOGY. 

cm.  cubes)  in  a  small  glass  jar  containing  freshly  prepared  Golgi's  mix- 
ture (p.  21),  which  is  to  be  covered  and  stood  in  the  dark  (in  winter 
it  must  be  put  in  an  oven  having  a  temperature  of  about  25°  C).  In 
from  one  to  two  hours  the  pieces  can  easily  be  cut  into  slices  about  4  mm. 
in  diameter.  The  quantity  of  Golgi's  fluid  to  be  used  is  regulated 
by  the  number  of  the  slices,  each  slice  requiring  about  10  c.c.  of  the 
mixture.  In  from  two  to  six  days,  less  often  fifteen  days,*  the  slices 
are  taken  out,  quickly  washed  for  a  couple  of  seconds  in  distilled  water, 
gently  dried  with  filter-paper,  and  placed  in  0.75  per  cent,  silver  solution 
(30  c.c.  of  the  I  per  cent,  solution  [p.  22]  plus  10  c.c.  of  distilled  water, 
and  for  each  piece  10  c.c.  of  this  fluid). f  A  brown  precipitate  imme- 
diately envelops  the  pieces.  They  should  be  left  in  the  silver  solution 
for  two  days  (which  need  not  stand  in  the  dark  and  must  not  be  placed  in 
the  oven),  and  they  may  remain  in  it  for  six  days  without  injury  ;  they 
are  then  placed  for  from  fifteen  to  twenty  minutes  (not  longer)  in  20  c.c. 
of  absolute  alcohol,  then  embedded  in  elder-pith  (or  in  celloidin,  see 
Microtome  Technic)  and  cut  into  thick  sections. 

Each  section  should  be  at  once  examined,  zvithont  a  cover-glass, 
with  the  low  power,  in  order  to  ascertain  its  usefulness  ;  if  it  is  good  it 
is  placed  for  from  one  to  two  minutes  in  a  watch-glass  containing  abso- 
lute alcohol,  then  for  a  few  minutes  in  carbol-xylol,  then  transferred  to 
the  slide.  The  xylol  is  removed  by  light  pressure  on  the  section  with 
clean  filter-paper  and  the  preparation  covered  with  a  few  drops  of  xylol- 
balsam.  A  cover-glass  must  not  be  applied,  because  it  would  prevent 
evaporation  of  the  moisture  in  the  section,  which  when  retained  destroys 
the  Golgi  preparations.  Not  infrequently,  especially  when  the  carbol- 
xylol  has  not  been  satisfactorily  removed,  the  xylol-balsam  gradually 
withdraws  from  the  preparation,  which  in  consequence  appears  Spoiled, 
but  may  be  fully  restored  by  the  application  of  a  fresh  drop  of  balsam. 
At  first  the  preparation  should  be  examined  with  the  low-power  objec- 
tive ;  when  the  balsam  has  become  dry  the  high  power  may  be  used. 

until  they  are  to  be  sectioned,  and  will  keep  in  good  condition  for  about  ten  months.  Then 
transfer  them  directly  into  95  per  cent,  alcohol  for  one  hour;  into  alcohol-ether  (equal  parts) 
for  a  half  hour  ;  into  thin  celloidin  solution  (in  alcohol-ether)  for  one  hour.  Mount  on  a  block 
with  thick  celloidin  solution  (see  Microtome  Technic)  and  harden  in  80  per  cent,  alcohol  for 
from  one  to  two  hours.  Cut  at  once  sections  from  50  to  loo  /z  thick  ;  clear  them  in  a  mixture 
of  xylol,  three  parts,  and  carbolic  acid,  one  part,  in  which  they  may  remain  for  weeks  without 
injury.  Mount  in  balsam  and  cover  the  sections  with  a  cover-glass.  In  time  the  specimens  thus 
preserved  are  not  infrequently  marred  by  the  appearance  of  corrosive  crystals,  but  the  impreg- 
nation of  the  elements  of  the  nervous  tissue  remains  intact. 

*  See  Special  Technic. 

f  The  used  Golgi  mixture  is  to  be  thrown  away. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  47 

The  results  obtained  by  this  method,  when  successful,  are  alto- 
gether admirable  ;  single  elements  of  the  nervous  system  (never  all), 
occasionally  also  blood-vessels,  lymph-vessels,  connective-tissue  fibers, 
secretions,  muscle-fibers,  and  epithelial  cells  stand  out  in  full  relief,  black 
on  a  light  background.  But  the  method  is  subject  to  various  accidents. 
Almost  invariably  the  best  sections  are  disfigured  by  black  precipitates  ; 
these  occur  chiefly  at  the  edges  of  the  preparation  ;  in  order  to  avoid 
them  it  has  been  suggested  that  a  layer  of  coagulated  blood  be  applied 
to  the  fresh  object.  Very  often  the  reaction  fails  entirely,  especially 
when  the  action  of  the  Golgi  mixture  was  too  prolonged  ;  then  the  so- 
called  "  double  method  "  may  lead  to  success.  If  the  first  sections  show 
nothing,  the  objects  should  be  again  treated  with  Golgi's  fluid  for  from 
twenty-four  to  thirty-six  hours  and  for  the  same  length  of  time  with  the 
silver  solution.  A  second  failure  may  be  occasionally  crowned  with 
success  by  a  second  repetition  of  the  procedure.  In  the  application  of 
Golgi's  method  practice  and  patience  are  important  factors. 

Instead  of  the  costly  Golgi  mixture  (p.  21)  potassium-bichromate- 
formol  (p.  21)  can  be  used.  Put  pieces  of  tissue  of  ca.  2  cm.  diameter 
in  50  c.c.  of  Kopsch's  fluid  (do  not  place  in  the  oven)  and  after  24  hours 
transfer  to  3.5  per  cent,  bichromate  solution  (10  b,  p.  21)  and  let  them 
remain  in  this  for  from  3  to  6  days.  Treatment  with  the  silver  solution 
is  the  same  as  after  fixation  with  the  osmium-bichromate  mixture.  Even 
with  material  48  hours  old  the  impregnation  still  succeeds. 

Impregnated  preparations  that  have  been  treated  either  with  the 
osmium  or  the  formol-bichromate  mixture  can  be  further  fixed  and 
stained.  For  this  purpose  transfer  the  sections  from  the  alcohol  to  a 
mixture  of  100  c.c.  of  0.75  per  cent,  salt  solution  (p.  20)  and  200  c.c. 
of  95  per  cent,  alcohol  (these  large  quantities  are  indispensable),  and 
stir  them  about  frequently  with  a  glass  rod,  for  a  period  of  from  10  to 
15  minutes  ;  next  place  them  in  a  glass  capsule  containing  about  20  c.c. 
of  80  per  cent,  alcohol  and  let  them  stand  on  a  white  background,  in 
the  hght  (not  in  sunlight),  for  a  half  day.  By  this  means  the  black 
precipitates,  that  in  the  alcohol-salt  mixture  very  rapidly  faded  to  a  pale 
yellow,  become  dark  again.  Then  stain  with  carmalum  (p.  39)  or  with 
Delafield's  hematoxylin  (p.  42).  In  staining  the  parietal  cells  (cf. 
Technic  No.  108)  use  also  eosin  (3  b,  p.  39).  Preparations  so  fixed  and 
stained  can  be  preserved  in  xylol-balsam  and  covered  with  a  cover- 
glass. 

18.  Gold  staining. — For  the  demonstration  of  nerve  terminations. 
Steel  instruments  must  not  be  used  ;  all  manipulations  in  the  gold  solu- 
tion are  to  be  performed  with  rods  of  glass  or  wood.      Put  8  c.c.   of  a   i 


48  HISTOLOGY. 

per  cent,  gold-chlorid  solution  and  2  c.c.  of  formic  acid  into  a  test-tube 
and  heat  the  mixture  to  the  boiling-point ;  let  it  boil  up  three  times. 
Into  the  c oo/ed  mix.ture  very  small  cubes  of  tissue  (at  most  5  mm.  square) 
are  placed  for  one  hour,  during  which  they  must  be  kept  in  the  dark  ; 
then  they  are  washed  in  distilled  water  and  exposed  to  the  light  in  a 
mixture  of  formic  acid,  10  c.c,  and  distilled  water,  40  c.c.  Sunlight  is 
not  necessary.  The  reduction  takes  place  slowly,  often  not  until  after 
twenty-four  or  forty-eight  hours,  the  exterior  of  the  cubes  meanwhile 
assuming  a  dark  violet  hue.  When  the  reduction  is  completed  place 
the  tissue  in  30  c.c.  of  70  per  cent,  alcohol,  and  on  the  following  day  in 
an  equal  quantity  of  90  per  cent,  alcohol,  in  which,  to  hinder  further  re- 
duction, they  must  remain  in  the  dark  for  at  least  eight  days  before  their 
final  preparation. 

§  9.   INJECTING. 

The  filling  of  the  blood-  and  lymph-vessels  with  colored  masses  is 
a  special  art  that  can  only  be  acquired  through  much  practice.  The 
knowledge  of  the  many  little  devices  employed  can  scarcely  be  attained 
through  didactic  teaching,  however  painstaking  and  explicit.  Here  prac- 
tical instruction  is  indispensable.  Accordingly,  since  this  book  is  intended 
for  beginners,  it  seems  wise  to  refrain  from  entering  upon  a  detailed 
account  of  the  technic  of  injecting. 

He  who  desires  to  attempt  injecting  must  have  an  accurately  closing, 
smoothly  working  hand-syringe,  provided  with  cannulse  of  different  sizes. 
For  an  injecting  mass  I  advise  Berlin  blue  (Griibler),  3  gm.  dissolved 
in  600  c.c.  of  distilled  water.  It  is  best  to  begin  with  the  injection  of 
single  organs,  for  example,  the  liver,  which  is  preferable  because  it  gives 
useful  results,  even  though  the  blood-vessels  are  but  partially  filled. 
The  injected  object  should  be  fixed  for  from  two  to  four  weeks  in 
Miiller's  fluid  (p.  33)  and  hardened  in  gradually  strengthened  alcohols 
(p.  35).  The  sections  must  not  be  too  thin.  For  injecting  the  lymph- 
vessels  Chinese  tusche  is  recommended  (see  Lendorf,  Anatom.  Hefte, 
Bd.  17,  p.  370). 

§  10.  MOUNTING  AND  PRESERVING  OF  THE 
PREPARATIONS. 
The  finished  sections  and  other  objects  prepared  according  to  the 
foregoing  methods,  in  order  that  they  may  be  examined  under  the  micro- 
scope, are  finally  mounted  on  a  slide  and  covered  with  a  cover-glass. 
The  media  in  which  the  sections  are  mounted  are  :  (i)  water ;  or,  if  the 
section  is  to  be  cleared  and  preserved,  {2)  glycerol ;  or  (3)  xylol-balsam. 


THE    PREPARATIDN    OF    MICROSCOPIC    SPECIMENS,  49 

The  transfer  of  the  object  to  the  slide  is  usually  done  in  this  way  : 
a  small  drop  of  a  suitable  fluid  is  placed  on  the  middle  of  the  slide  ;  the 
section  is  then  taken  up  on  the  section-lifter  and  with  the  aid  of  the 
needle  slipped  off  onto  the  slide.  Very  thin  sections  are  better  lifted  on 
the  end  of  a  glass  rod  and  by  rolling  of  the  latter  transferred  to  the 
slide.  When  the  section  is  smoothly  mounted,  it  is  covered  with  a 
cover-glass.*  The  latter  must  be  grasped  by  its  edges,  not  by  its  sur- 
faces. It  should  be  taken  in  the  left  hand,  one  edge  placed  in  contact 
with  the  slide,  and  then,  supported  on  its  under  surface  by  a  needle  held 
in  the  right  hand,  slowly  lowered  upon  the  preparation.  It  is  simpler 
to  suspend  a  drop  of  the  mounting  medium  from  the  under  surface  of 
the  cover-glass  and  then  to  let  it  softly  fall  upon  the  preparation. 
The  fluid  in  which  the  section  is  mounted  must  occupy  the  entire  space 
between  cover-glass  and  slide.  If  the  amount  of  fluid  is  insufficient, 
which  is  recognized  by  the  large  air-bubbles  under  the  cover-glass,  another 
drop  should  be  placed  at  one  edge  of  the  cover-glass  by  means  of  a 
pointed  glass  rod.  If  there  is  too  much  fluid — here  the  beginner  strives 
to  perpetrate  impossibilities — the  excess  which  has  escaped  from  be- 
neath the  edges  of  the  cover-glass  should  be  absorbed  with  filter-paper. 
The  upper  surface  of  the  cover-glass  must  ahvays  be  dry.  Small  air-bub- 
bles under  the  cover-glass  may  be  removed  by  cautiously  raising  and 
lowering  the  cover  several  times  Avith  the  needle  (see  further,  p.  51). 

1.  The  examination  of  the  unstained  and  the  stained  sections  in  zvater 
or  normal  salt  solution  should  never  be  neglected,  since  many  structural 
peculiarities — for  example,  connective-tissue  formations — stand  out  dis- 
tinctly in  these  media,  which  under  the  clearing  influence  of  glycerol  or 
xylol-balsam  almost  entirely  elude  observation.  Preparations  mounted 
in  water  or  salt  solution  cannot  be  preserved. 

2.  Preparations  mounted  in  glycerol  can  be  preserved  ;  in  order  to 
prevent  the  shifting  of  the  cover-glass  it  should  be  secured  with  cover- 
glass  cement  (p.  23).  The  edge  of  the  cover-glass  must  be  perfectly  dry  ; 
this  is  an  indispensable  preliminary  condition,  because  the  cement  adheres 
only  to  a  dry  glass  surface.  The  drying  is  accomplished  in  this  wise  : 
remove  the  excess  of  glycerol  surrounding  the  cover-glass  with  filter- 
paper  and   then   with  a  cloth   moistened   in  90  per  cent,    alcohol   and 

*  Examinations  with  low  powers,  without  a  cover-glass,  are  permissible  only  for  the  most 
superficial  orientation  :  e.  g.,  to  ascertain  if  an  object  has  been  sufficiently  teased.  In  all  other 
cases  the  cover-glass  is  indispensable.  In  order  to  convince  one's  self  of  this  ^n  uncovered  sec- 
tion should  be  examined,  then  covered  with  a  cover-glass  and  examined  again.  Many  a  good 
preparation  that  one  neglects  to  cover  appears  useless.  Examinations  with  high-power  objec- 
tives without  a  cover-glass  are  in  general  not  allowable  ;  they  should  only  be  attempted  with 
certain  methods,  e.  g.,  Golgi's. 
4 


50  HISTOLOGY. 

turned  over  the  finger-tip  carefully  wipe  the  slide  clean  all  around  the 
cover-glass  without  disturbing  the  latter.  Heat  a  glass  rod  and  thrust 
it  into  the  hard  cement ;  *  place  a  drop  at  each  corner  of  the  cover- glass 
and  trace  a  continuous  band  from  i  to  3  mm.  wide,  in  such  a  way  that 
one  edge  rests  on  the  cover-glass,  the  other  on  the  slide.  Finally,  re- 
heat the  rod  and  smooth  the  surface  of  the  band  of  cement. f 

Preparations  mounted  in  glycerol  often  do  not  become  transparent 
until  the  second  or  third  day.  Hematoxylin  and  other  dyes  soon  fade 
in  it ;  picrocarmine  and  carmine,  on  the  contrary,  are  permanent. 

3.  The  mounting  of  objects  in  xylol-balsam  is  the  most  popular  pre- 
serving method.  In  comparison  with  glycerol  it  has  the  advantage  of 
keeping  the  colors,  but  has  one  disadvantage  :  it  clears  more  vigorously 
than  diluted  glycerol,  and  thus  renders  many  delicate  structures  com- 
pletely invisible. 

Sections  in  alcohol  or  water  cannot  without  further  treatment  be 
mounted  in  balsam  ;  they  must  be  previously  dehydrated.  For  this  pur- 
pose the  sections  are  lifted  with  a  needle  (very  thin  sections  with  needle 
and  section-lifter)  and  placed  in  a  covered  Avatch-glass  containing  5  c.c. 
of  95  per  cent,  alcohol.  In  making  this  transfer  as  Httle  as  possible  of 
the  water  should  be  allowed  to  adhere  to  the  section.  If  a  section-lifter 
is  used,  the  water  clinging  to  it  should  be  absorbed  with  filter-paper  ;  if 
the  sections  are  lifted  on  a  needle,  the  water  can  be  removed  by  bringing 
the  filter-paper  into  gentle  contact  with  them.  Thin  sections  remain  in 
the  95  per  cent,  alcohol  two  minutes  ;  thick  sections,  ten  minutes  or 
more. I  Then  the  sections  are  transferred  for  clearing  to  a  watch-glass 
containing  3  c.c.  of  carbol-xylol  §  or  xylol,  ||  as  much  as  possible  of  the 
alcohol  being  removed  with  filter-paper  before  placing  them  in  the  clear- 

*  Glass  rods  fracture  very  easily  in  this  procedure,  nevertheless  are  preferable  to  metal 
rods,  because  the  latter  cool  too  quickly.  The  fracturing  can  be  prevented  in  a  measure  by 
heating  the  glass  rod  to  redness,  meanwhile  turning  it  continuously  ;  only  rods  insufficiently  an- 
nealed break  when  they  are  dipped  into  the  cement. 

I  Editor'' s  remark:  King's  fluid  cover-glass  cement  (p.  23,  foot-note)  is  to  be  applied 
with  a  small  brush. 

\  Beginners  are  recommended  to  transfer  the  sections  from  the  water  to  5  c.c.  of  90  per 
cent,  alcohol,  and  then  to  place  them  in  an  equal  quantity  of  95  per  cent,  alcohol. 

\  Thin  sections  may  be  transferred  from  the  95  per  cent,  alcohol  directly  on  to  the  slide, 
the  superfluous  alcohol  removed  by  means  of  absorbent  paper,  and  a  drop  of  carbol-xylol  applied. 
At  first  the  xylol  will  retreat  from  the  section  and  must  be  led  back  with  the  needle ;  when  the 
clearing  is  completed,  which  can  be  ascertained  under  the  microscope  with  the  low  power,  the 
xylol  should  be  absorbed  with  filter-paper  and  a  cover-glass  with  a  drop  of  balsam  applied. 
When  examining  uncovered  sections  lying  in  xylol  both  xylol  and  section  often  become  clouded 
by  the  moisture  exhaled  in  breathing  ;  in  this  case  drain  off  the  clouded  xylol  and  add  a  fresh  drop. 

II  On  account  of  its  greater  sensitiveness  to  water  and  because  it  evaporates  so  easily  the 
manipulation  with  xylol  is  more  difficult.  Many  a  good  preparation  spoils  at  the  last  moment, 
because  the  xylol  has  been  allowed  to  evaporate. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  5 1 

ing  agent.  If  the  watch-glass  is  placed  on  a  black  background  the 
effect  of  the  oil  can  be  watched,  and  it  will  be  seen  that  the  sections 
gradually  become  transparent.  Care  must  be  taken  not  to  breathe  into 
the  watch-glass,  or  the  xylol  will  immediately  become  turbid.  If 
some  areas  of  the  section  do  not  become  transparent  within  two 
or  three  minutes  (such  areas  appear  white  and  opaque  in  direct 
light,  black-brown  in  transmitted  light),  this  indicates  that  the  section 
is  not  dehydrated  and  it  must  be  put  back  into  absolute  alcohol. 
When  the  clearing  is  completed  the  section  is  transferred  to  a  dry  slide, 
the  superfluous  xylol  *  absorbed  by  gentle  pressure  with  a  strip  of 
smooth  filter-paper, t  and  a  cover-glass,  on  the  under  surface  of  which 
a  drop  of  balsam  is  suspended,  applied.  If  several  sections  are  to  be 
mounted  under  one  cover,  arrange  them  close  together  with  a  needle  ; 
then,  by  means  of  a  glass  rod,  apply  a  thin,  even  layer  of  balsam  to  the 
under  surface  of  the  cover-glass  and  place  it  on  the  sections.  Large 
air-bubbles  are  driven  out  by  placing  a  small  drop  of  balsam  at  the 
edge  of  the  cover-glass  ;  on  the  following  day  it  will  be  seen  that  the  air- 
bubbles  have  retreated  from  beneath  the  cover.  Small  air-bubbles  dis- 
appear spontaneously  and  may  be  neglected. 

It  not  infrequently  happens  to  beginners  to  discover  that  the  balsam 
becomes  turbid,  and  finally  renders  the  entire  preparation,  or  parts  of  it, 
untransparent.  This  is  due  to  incomplete  dehydration.  If  the  clouding  is 
slight,  which  under  the  microscope  is  seen  to  consist  of  minute  drops  of 
water,  a  gentle  warming  of  the  slide  is  often  sufficient  to  remove  it.  In 
the  case  of  much-clouded  preparations,  place  the  whole  slide  in  carbol- 
xylol  for  half  an  hour  ;  then  carefully  lift  off  the  cover-glass,  place  the 
section  for  two  minutes  in  carbol-xylol,  in  order  to  dissolve  off  the  ad- 
herent balsam,  and  then  dehydrate  in  4  c.c.  of  absolute  alcohol,  which 
should  be  changed  in  five  minutes  ;  clear  in  carbol-xylol  and  mount  in 
balsam. 

The  balsam  dries  slowly,  therefore  the  slides  must  not  be  stood  on 
edge,  but  be  kept  in  a  horizontal  position. 

The  series  of  processes  through  which  a  fresh  object  must  pass 
until  it  is  preserved  as  stained  sections  is  a  very  long  one.  When,  for 
example,  the  directions  in  the  Special  Technic  require  "fixation  in 
Zenker's  fluid,  hardening  in  gradually  strengthened   alcohols,  staining  of 

*  The  carbol-xylol  in  the  watch-glass  that  has  been  used  for  clearing  may  be  returned  to 
the  bottle. 

f  The  double  folded  strip  is  held  fast  by  the  left  hand  to  the  left  end  of  the  slide  and, 
lying  upon  the  preparation,  is  gently  stroked  from  left  to  right  by  the  index  finger  of  the  right 
hand. 


52  HISTOLOGY. 

sections  in  hematoxylin   and  e6sin,  and  mounting  in  balsam,"  the  pro- 
cedure is  as  follows  : 

1.  Place  the  fresh  object,  about  i  cm.  in  diameter,  in  60  c.c.  of 
Zenker's  fluid  *  for  twenty-four  hours. 

2.  Wash  in  (if  possible  running)  water  for  twenty-four  hours. 

3.  Place  in  20  c.c.  of  distilled  water  for  about  fifteen  minutes. 

4.  Transfer  to  50  c.c.  of  50  per  cent,  alcohol  for  twenty-four 
hours  ;    from   now  on   the  object  is  to   be  kept   in  the  dark. 

5.  Transfer  to  50  c.c.  of  70  per  cent,  alcohol  for  twenty-four  hours. 

6.  Transfer  to  50  c.c.  of  90  per  cent,  alcohol  and  tincture  of  iodin 
for  from  eight  to  fourteen  days,  daily  adding  tincture  of  iodin. 

7.  Transfer  to  pure  90  per  cent,  alcohol,  which  is  to  be  changed 
two  or  three  times. 

The  object  thus  fixed  and  hardened  can  be  sectioned  at  once  or  may 
remain  indefinitely  in  the  90  per  cent,  alcohol,  which  perhaps  should  be 
once  renewed. t 

8.  Transfer  the  sections  from  the  alcohol  to  5  c.c.  of  hematoxylin 
for  five  minutes. 

9.  Transfer  to  30  c.c.  of  distilled  water  for  from  ten  minutes  to  two 
hours. 

10.  Stain  in  5  c.c.  of  diluted  eosin  for  from  one  to  three  minutes. 

11.  Wash  in  5  c.c.  of  distilled  water  for  two  minutes. 

12.  Dehydrate  in  5  c.c.  of  absolute  alcohol  for  five  minutes. 

13.  Clear  in  5  c.c.  of  carbol-xylol  for  five  minutes. 

14.  Mount  in  xylol-balsam. 


§   II.  EXAMINATION  OF    FRESH  OBJECTS. 

I  have  placed  this  method  last  because  it  is  the  most  difficult  and 
presupposes  a  somewhat  practised  eye.  This  practice  is  most  readily 
acquired  by  previous  examination  of  prepared  (hardened,  stained,  etc.) 
objects  ;  having  once  clearly  perceived  and  studied  peculiarities  of  struc- 
ture it  is  then  not  difficult  to  detect  them  in  fresh  objects,  even  though 
the  majority  of  the  details  leave  something  to  be  desired  in  point  of  dis- 
tinctness.     The  following  instructions  should  be  observed  : 

The    slide  and  cover-glass    must  not  be    oily.       They    should  be 


*  The  quantities  named  are  calculated  only  for  this  i  cm.  cube  ;   for  several  or  for  larger 
objects  more  fixing  and  more  hardening  fluid  must  be  used. 

iThe  following  quantities  are  intended  for  from  three  to  six  sections  ;  for  a  larger  number 
of  sections  the  quantity  of  the  absolute  alcohol  in  particular  should  be  increased. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  53 

cleansed  with  alcohol  and  dried  with  a  perfectly  clean  cloth.*  Then 
transfer  one  drop  of  a  0.75  per  cent,  salt  solution  (p.  20)  to  a  slide, 
place  in  it  a  small  piece  of  the  object  to  be  examined  and  cover  it  with  a 
cover-glass.  Pressure  must  be  carefully  avoided  ;  if  the  structures  are  very 
delicate  support  the  cover-glass  on  two  strips  of  thin  paper  placed  at  the 
sides  of  the  object.  If  the  object  requires  no  further  treatment  the 
cover-glass  should  be  sealed  with  paraffin  to  prevent  evaporation.  Melt 
a  small  piece  of  paraffin  on  the  blade  of  an  old  scalpel  and  let  it  flow, 
not  from  the  tip  but  from  the  edge,  on  to  the  rim  of  the  cover-glass  ; 
gaps  that  may  occur  in  this  frame  of  paraffin  can  be  closed  with  the  re- 
heated scalpel.  In  most  cases  the  influence  of  certain  reagents  (acids, 
alkalies,  stains)  is  studied  directly  under  the  microscope.  It  is  then 
necessary  to  remove  a  portion  of  the  medium  in  which  the  object  happens 
to  -be  mounted  (in  the  present  instance  the  salt  solution)  and  to  replace 
it  by  another  fluid.  For  this  purpose  place  a  drop  of  picrocarmine  at 
the  right  edge  of  the  cover-glass,  by  means  of  a  glass  rod.  Should  the 
drop  not  touch  the  q^^q  of  the  cover-glass,  do  not  incline  the  slide,  but 
lead  it  with  a  needle  to  the  appropriate  position.  It  may  now  be  seen 
that  a  little  of  the  staining  fluid  mingles  with  the  salt  solution,  but 
does  not  properly  flow  under  the  cover-glass.  In  order  that  this  shall 
occur  place  at  the  left  edge  of  the  cover-glass  a  little  piece  of  filter- 
paper  f  and  immediately  the  picrocarmine  will  be  seen  to  diffuse  under 
the  cover-glass  and  occupy  the  entire  area.|  Then  remove  the  filter- 
paper  and  let  the  stain  act ;  when  the  staining  is  completed, — this  can  be 
ascertained  under  the  microscope, — place  at  the  right  edge  of  the  cover- 
glass  a  drop  of  diluted  glycerol  to  which,  in  picrocarmine  staining,  as 
much  acetic  acid  is  added  as  will  drop  from  a  steel  needle  (hence  a 
very  small  drop),  and  again  apply  the  filter-paper  to  the  left  &A^&  of  the 
cover-glass.  In  this  way  a  whole  series  of  fluids  can  be  passed  through 
beneath  the  cover-glass  and  their  action  on  the  tissues  tested.  Some  of 
these  fluids,  for  example,  picrocarmine,  must  remain  in  contact  with  the  ob- 
jects for  a  very  long  time  if  they  have  been  previously  fixed  with  osmic 
acid.  In  this  case  evaporation  is  prevented  by  placing  the  object  in  a 
vioist-chainhcr.      For  the   construction   of  a   moist-chamber  a  porcelain 


*  For  removing  the  oil  from  new  cover-glasses,  heating  them  on  a  piece  of  sheet-iron  for 
five  minutes  over  the  flame  of  a  Bunsen  burner  is  recommended. 

f  Cut  a  strip  4  cm.  long  and  2  cm.  broad,  fold  it  square,  and  place  the  paper  tent  thus 
formed  on  the  slide,  so  that  one  of  the  2  cm.  ends,  which  must  \>&  pei-fectly  straight^  touches  the 
left  edge  of  the  cover-glass. 

j  After  the  first  drop  has  penetrated  place  two  or  three  additional  drops  at  the  right  edge 
of  the  cover-glass. 


54  HISTOLOGY. 

plate  and  a  small  bell-glass  9  cm.  in  diameter  are  required.  Pour  water 
into  the  plate  to  the  depth  of  2  cm.  and  stand  in  the  middle  a  small  glass 
dish  or  a  cork  disk  supported  on  wooden  pegs  ;  on  the  latter  place  the 
slide  with  the  preparation  and  cover  the  whole  with  the  glass  bell,  the 
free  edge  of  which  must  be  submerged  in  the  water. 


§    12.  STORING  OF  PERMANENT  PREPARATIONS. 

The  finished  preparations  should  be  promptly  labeled.  Labels  of 
cardboard  about  1.2  mm.  thick,  glued  to  the  slide  with  fish-glue  (isinglass) 
are  preferable  to  those  of  gummed  paper  ;  the  slides  can  then  be  placed 
one  upon  the  other  without  injury  to  the  preparations.  The  labels 
should  be  as  large  as  possible  (2  cm.  square  for  slides  of  EngHsh  form) 
and  should  bear  the  name  of  the  animal,  of  the  organ,  and  if  possible  a 
brief  statement  of  the  method  used.  Of  the  cases  *  for  storing  the  prep- 
arations only  such  should  be  chosen  in  which  the  slides  lie  flat,  not 
those  in  which  they  stand  on  edge. 


*The  best  and  cheapest  cases  are  made  by  Th.  Schroter,  Leipzig,  Connewitz.  I  recom- 
mend for  box  ioxm  pattern  O  (for  about  300  slides),  price  2  M.  (50  cents)  ;  for  tray  form,  F, 
with  spring  covers  (for  10  to  20  slides  according  to  size),  price  45  Pfg.  (about  12  cents).  The 
tray  form  has  the  great  advantage  of  allowing  all  the  specimens  to  be  seen  at  once.  In  the 
United  States  Schroter's  boxes  and  trays  are  supplied  by  King  &  Co.,  New  York,  the  Bausch 
&  Lornb  Optical  Co.,  New  York,  and  other  dealers. 


III.  MANAGEMENT  OF  THE  MICROSCOPE. 

In  conformity  with  the  position  taken  in  the  introduction,  an  ex- 
haustive description  of  the  optic  and  mechanic  parts  of  the  microscope 
cannot  be  entered  upon  here.  Figure  i  will  recall  to  the  reader  the 
usual  names  of  the  several  parts  of  the  microscope. 

The  first  requisite  in  the  use  of  the  microscope  is  perfect  cleanliness 
of  all  its  parts  (see  also  p.  17).  The  surface  of  the  mirrors,  objectives, 
and  oculars  should  not  be  touched  with  the  fingers.  The  objective 
should  be  held  with  the  lower  end  directed  toward  the  window  and  the 
clearness  of  the  reflected  image  thus  tested.  Foreign  matter  on  the 
ocular  can  be  detected  by  rotating  the  latter  in  the  tube,  when  anything 
that  is  adherent  will  revolve. 

After  the  ocular  has  been  placed  in  the  upper  end  of  the  draw-tube 
and  a  low-power  objective  screwed  on  the  lower  end  of  the  tube  or  on 
the  revolver,  the  field  of  view  should  be  illuminated  with  light  reflected 
from  a  suitable  source  by  the  concave  mirror  placed  below  the  stage. 
This  is  accomplished  by  moving  the  mirror  tentatively  in  all  directions, 
with  the  diaphragm  widely  open  and  the  front  lens  of  the  objective 
about  I  cm.  above  the  level  of  the  stage,  till  the  eye,  looking  simul- 
taneously through  the  eye-piece  into  the  microscope,  sees  the  field 
brightly  and  uniformly  lighted.*  The  concave  mirror  should  be  used 
with  dry  lenses,  except  when  a  substage  condenser  is  employed. 

The  light  reflected  from  a  white  cloud  or  from  a  white  window- 
blind  illuminated  by  the  sun  is  recommended  ;  less  desirable  but  still  use- 
ful as  a  source  of  light  is  the  blue  sky.  Direct  sunlight  must  be 
avoided.  In  using  artificial  illumination  the  light  should  be  taken  from 
the  inner  surface  of  a  white  lamp-shade,  not  directly  from  the  flame. 
A  screen  of  green  glass  placed  between  the  mirror  and  the  source  of 
light,  or  between  the  mirror  and  the  object,  agreeably  subdues  artificial 


*The  rays  of  light  reflected  from  the  mirror  in  this  position  pass  perpendicularly  through 
the  object  on  the  stage.  This  is  called  central  ilhiminalio7i.  For  distinguishing  slight  differ- 
ences of  level  between  adjacent  parts  of  an  object  it  is  of  advantage  to  use  oblique  or  lateral 
ilhunination,  to  obtain  which  the  mirror  is  moved  to  the  side  so  that  the  rays  reflected  from  it 
strike  the  object  obliquely.  When  lateral  illumination  is  used  the  diaphragm  and  the  cylinder 
in  which  it  is  mounted  must  be  removed,  that  the  opening  in  the  stage  be  as  large  as  possible. 

55 


56 


HISTOLOGY. 


Eye-piece  (Ocular) 


•   •  Draw-tube 


I     1   md  pinion  adjustment 


Triple  revolver 
Objective 


Micrometer  Screw 


Fig.  I.— Leitz  Microscope.    Stand  II  (one-half  actual  size). 

light,  without  essentially  injuring  the  definition  of  the  image.  It  is  self- 
evident  that  the  microscopist  should  not  sit  in  direct  sunlight ;  the  in- 
strument should  be  placed  about  a  meter  trom  the  window. 


MANAGEMENT    OF    THE    MICROSCOPE.  57 

Having  secured  the  light  the  examination  may  begin.  Akuays  ex- 
amine first  with  the  low-power,  then  witJi  tlie  high-pozuer  objective  ;  do  not 
use  strong  oculars  ;  they  narrow  and  darken  the  field  of  view  and  render 
the  examination  much  more  difficult.*  The  low-  and  medium-power 
oculars  (Leitz,  Oc.  I)  of  the  usual  outfit  supplied  with  the  microscope 
answer  for  the  great  majority  of  cases. 

The  increased  magnification  obtained  by  pulling  out  the  draw-tube 
is  seldom  necessary.  With  low-power  lenses  a  diaphragm  having  a 
large  opening  should  be  used  ;  with  high-power  lenses  a  diaphragm 
having  a  small  opening.  In  focusing  the  object  the  coarse  adjustment 
by  rack  and  pinion  is  used  first  ;  the  objective  is  placed  near  to  the 
object,  but  at  a  distance  greater  than  its  focal  length  and  then,  with  the 
eye  applied  to  the  ocular,  the  tube  is  gradually  lowered  until  the  indis- 
tinct outhnes  of  the  image  appear,  which  is  then  brought  into  distinct 
view  by  means  of  the  fine  adjustment  or  micrometer-screw.  The  left 
hand  should  hold  the  slide,  while  the  right  should  remain  at  the  microm- 
eter-screw. Since  only  the  points  lying  in  a  single  plane  of  the  object 
can  be  in  focus  and  distinctly  seen  at  one  time,  the  preparation  must  be 
examined  with  slight  raising  and  lowering  of  the  tube,  that  is,  with 
change  of  focus  by  gently  turning  the  micrometer-screw.  In  using  the 
microscope  the  habit  should  be  formed  of  keeping  both  eyes  open. 

One  should  never  neglect  to  examine  the  preparations  with  a  hand- 
lens.  For  this  purpose  the  oculars  {e.  g.,  Leitz,  Oc.  Ill)  can  be  used. 
The  mounted  specimen  is  held  with  the  cover-glass  side  toward  the 
light ;  the  upper  or  back  lens  of  the  ocular  is  placed  directly  against  the 
slide,  which  is  examined  at  the  lower  or  front  lens. 

SKETCHING. 
An  invaluable  aid  to  study  is  the  sketching  of  the  microscopic 
object.  The  power  of  observation  is  made  considerably  keener  and  many 
details  which  otherwise  would  be  completely  overlooked  are  discovered 
while  the  sketch  is  in  progress.  The  most  attentive  examination  can- 
not replace  the  advantages  which  sketching  affords.  Even  those  who 
have  little  practice  in  drawing  should  nevertheless  try  to  sketch  the 
preparations  under  both  low-  and  high-power  objectives.  For  this  pur- 
pose the  drawing-paper  should  be  on  a  level  with  the  stage,  the  left  eye 
applied  to  the  microscope,  the  right  eye  directed  to  the  paper  and  the 
pencil-point.  At  first  this  is  somewhat  difficult,  but  a  little  practice  will 
soon  give  the  necessary  facility. 

*The  majority  of  the  preparations  from  which  the  illustrations  in  this  book  were  taken 
were  examined  and  sketched  with  weak  oculars. 


58  ,        HISTOLOGY. 


MEASUREMENT. 

For  this  purpose  an  ocular-micrometer  and  stage-micrometer  are 
used.*  The  latter  is  laid  on  the  stage  of  a  microscope  provided  with  an 
ocular-micrometer  and  the  number  of  divisions  of  the  ocular-micrometer 
corresponding  to  one  part  of  the  stage-micrometer  is  ascertained.f  The 
dimensions  of  the  spaces  of  the  stage-micrometer  being  known  the  size  of 
the  object,  which  with  a  given  magnification  will  occupy  one  or  more  of 
the  divisions  of  the  ocular-micrometer,  is  easily  calculated.  The  follow- 
ing illustrations  may  render  the  manipulation  intelligible. 

With  ocular  I  and  draw-tube  pushed  in  5  divisions  of  the  ocular- 
micrometer  correspond  with  one  division  of  the  stage-micrometer.  Each 
division  of  the  stage-micrometer  used  =  -^  mm.  Hence  5  divisions  of 
the  ocular-micrometer  =  -^-^  (0.05  mm.),  and  i  division  of  the  ocular- 
micrometer  =  0.0 1  mm.  If  then  any  microscopic  object,  e.g:,a.  striated 
muscle-fiber,  the  diameter  of  which  is  to  be  measured  with  this  magnifica- 
tion, occupies  4  divisions  the  fiber  is  0.04  mm.  broad. 

It  is  often  difficult,  especially  with  low  magnification,  to  count  the 
fine  divisions  of  the  ocular-micrometer.  This  can  be  more  easily  done 
by  noting  the  longer  lines  marking  every  fifth  or  tenth  division.  For  in- 
stance, with  Leitz  Objective  3,  Ocular  I,  and  the  draw-tube  drawn  out, 
40  divisions  of  the  ocular-micrometer  correspond  with  5  divisions  of  the 
stage -micrometer.  Therefore,  40  divisions  =  -^-^  mm.  =  O.25  mm.,  and 
one  division  of  the  ocular-micrometer  with  this  magnification  =  0.0062 
mm.,  2  divisions  =  0.0 124  mm.,  and  so  on. 

With  Leitz  Objective  7,  Ocular  I,  and  draw-tube  pushed  in,  30  divi- 
sions of  the  ocular-micrometer  correspond  with  one  division  of  the  stage- 
micrometer  ;  30  divisions  =  0.05  mm.,  one  division  =  0.0017  mm.,  or 
ly/jt.X  Finally,  with  Leitz  Objective  7,  Ocular  I,  and  draw-tube  drawn 
out,  40  divisions  of  the  ocular-micrometer  =  one  division  of  the  stage- 
micrometer.  Therefore,  40  divisions  =  0.05  mm.,  one  division  =  0.0012 
mm.,  or  1.2  fji. 

*  Some  ocular-micrometers  (Leitz)  are  made  to  rest  upon  the  diaphragm  inside  the  ocular; 
others  (Seibert)  to  be  inserted  through  a  lateral  opening ;  or,  in  some  cases,  special  oculars 
(Zeiss)  for  measuring  are  made  for  the  microscope.  The  actual  size  of  the  divisions  of  the 
ocular-micrometer  need  not  be  known.  The  stage-micrometer  is  a  glass  slide  on  which  I  mm. 
with  100  divisions  is  engraved.  Instead  of  this  a  second  ocular-micrometer,  which  usually 
contains  a  mm.  with  only  20  divisions,  may  be  used.  Measurements  made  with  this  are  not  as 
accurate,  but  the  errors  are  so  insignificant  that  they  scarcely  need  consideration. 

I  Beginners  often  find  it  difficult  to  focus  the  lines  on  the  stage- micrometer ;  faint  or 
oblique  illumination  of  the  object  makes  it  easier  to  detect  them. 

I  One  micron  =  /x  =  o.ooi  mm. 


MANAGEMENT    OF    THE    MICROSCOPE.  59 

He  who  has  many  microscopic  measurements  to  make  will  find  it 
useful  to  prepare  a  table  for  each  magnification  used,  in  which  the 
equivalent  values  of  i  to  20  and  from  this  in  tens  up  to  100  scale 
divisions  of  the  ocular-micrometer  are  given.  It  must  be  emphasized 
that  the  foregoing  calculations  by  no  means  apply  to  all  the  microscopes 
made  by  Leitz.  The  values  must  be  specially  determined  for  every  in- 
strument by  the  foregoing  method. 

In  conclusion  the  microscopist  is  advised  to  be  patient,  very  pa- 
tient;  if  his  preparations  are  unsuccessful  let  him  not  search  for  the  cause 
in  the  deficiency  of  the  methods  recommended, — I  have  often  tested 
them — but  in  himself;  he  who  cannot  accustom  himself  conscientiously 
to  follow  the  written  instructions,*  who  grasps  delicate  objects  with  his 
fingers,  who  contaminates  the  reagents  by  pouring  one  into  the  other, 
who  leaves  objects  in  fixing  fluids  exposed  to  the  sun  or  allows  them  to 
become  dry,  has  not  the  right  to  expect  good  results  from  his  slovfenly 
work. 


*  The  periods  of  time  given  for  staining,  dehydrating,  etc.,  have  only  an  approximate 
value.  They  vary  within  considerable  limits  in  accordance  with  the  thickness  of  the  sections, 
the  concentration  of  the  solutions,  etc.  Experience  will  soon  teach  the  microscopist  to  deter- 
mine the  precise  period  of  time. 


PART   II. 

MICROSCOPIC  ANATOMY  AND  SPECIAL 

TECHNIC. 

The  animal  body  consists  of  cells  which  are  derived  from  a  single 
cell  by  repeated  division.  At  the  beginning  of  development  the  cells  are 
of  similar  form,  all  are  spherical  structures,  none  is  furnished  with 
special  characteristics  that  distinguish  it  from  its  companions.  The  cells 
are   still  indifferent.     In    the    course  of  development  the  cells  arrange 


Central  canal. 


Body  cavity. 


Intestinal  cavity. 


Outer  germ-layer. 


Medullary  tube. 


Outer  1 


Inner 


Lamella  of  the 
middle  germ- 
layer. 


Inner  germ-layer. 


Fig.  2. — Schematic  Section  of  the  Body  of  a  Vertebrate  Embryo.    The  free  side  of  the  cells  is 

marked  by  deeper  shading. 

themselves  in  the  germ-layers ;  these  are  cell  complexes,  that  in  the 
lower  vertebrates  are  for  a  time  disposed  in  a  simple  stratum.  The 
germ-layers  thus  represent  an  epithelium,  that  is,  a  continuous  layer  of 
cells  which  covers  outer  and  inner  surfaces  of  the  body  ;  each  cell  is  an 
epitheHal  cell,  in  which  Tifree  side,  directed  toward  the  surface,  and  a 
basal  side  can  be  distinguished  (Fig.  2). 

In  the  further  course  of  development  the  germ-layers  become  par- 
tially stratified,  a  not  insignificant  number  of  cells,  entire  or  in  divisions, 
depart  from  the  epithelial  association,  whereby  the  cells  become  different 

60 


MICROSCOPIC    ANATOMY.  6  I 

from  one  another,  they  differentiate.  As  a  rule,  the  "differentiated" 
cells  that  have  developed  in  a  given  direction  are  united  in  complexes, 
without  definite  spatial  limitation,  and  so  form  a  tissue.  A  tissue,  there- 
fore, is  a  complex  of  similarly  differentiated  cells.  We  distinguish  four 
principal  tissues  :  (i)  the  epithelial  tissue ;  (2)  the  supporting  tissue ;  (3) 
the  muscular  tissue  ;  (4)  the  nervous  tissue.  Epithelial  tissue  can  be  de- 
veloped from  each  of  the  three  germ-layers.  Supporting  tissue  is  de- 
veloped only  from  the  middle  germ-layer,  the  mesoderm  ;  nerve  tissue 
only  from  the  outer  germ-layer,  the  ectoderm  ;  muscle  tissue,  in  by  far 
the  greater  part,  is  of  mesodermal  origin,  but  in  isolated  instances  of  ecto- 
dermal origin.  So  long  as  these  tissues  are  still  young  they  consist 
only  of  similar  elements,  only  of  cells  ;  but  in  the  process  of  develop- 
ment this  condition  is  modified  in  a  twofold  manner.  First,  the  cells 
produce  special  substances,  which  are  bestowed  between  cells  and  are 
called  intercelhdar  substances.  However,  thereby  the  character  of  the 
tissue  is  not  essentially  altered.  The  above  definition  of  "tissue  "  need 
be  only  so  extended  that  we  describe  a  tissue  as  a  complex  of  similarly 
differentiated  cells  and  their  derivatives.  More  radical  is  the  second 
modification,  which  consists  in  the  interpenetration  of  a  tissue  of  one 
kind  by  other  tissues.  This  occurs  in  very  different  degrees.  The 
epithelial  tissues  have  preserved  the  greatest  simplicity  and  following 
them  the  supporting  tissues.  But  muscle  and  nerve  in  the  matured  state 
are  so  largely  intermixed  with  other  tissues,  that  even  though  in  each  the 
elements  respectively  differentiated  to  muscles  and  nerves  predominate, 
yet  one  can  scarcely  speak  of  a  tissue  in  the  sense  of  the  given  defini- 
tion.* Therefore  the  tissues  are  not  equivalent  among  one  another. 
In  the  lowest  rank  stand  the  epithelial  and  the  supporting  tissue  ;  dif- 
ferent from  each  other,  respecting  their  form  as  well  as  their  function,  they 
both  occur  in  the  vegetable  world  and  therefore  we  can  class  them  as 
vegetative  tissues.  On  a  higher  level,  as  well  morphologically  as  physi- 
ologically, stand  the  muscle  and  nerve  tissues,  and  being  peculiar  to  the 
animal  organism  they  are  named  aninial  tissues. 

The  fact  that  the  tissues  originate  from  the  epithelial  germ-layers  does  not 
warrant  the  conclusion  that  after  complete  differentiation  of  the  chief  tissues 
supporting,  or  muscle,  or  nerve  tissue  can  arise  from  the  perfected  epithelial 
tissue.     Each  principal  tissue  then  furnishes  only  its  kind. 

When  different  tissues  unite  in  the  formation  of  a  body  of  definite 
internal  structure  and  definite  external  form  f  they  constitute  an  organ. 

*  For  this  reason  the  proposition  has  been  made  to  take  exception  to  the  classification  in 
tissues  and  to  distinguish  only  elements  and  organs. 

f  Usually  in  the  definition  of  an  organ  "  the  definite  function  "  is  included  ;  but  this  does 
not  come  within  the  limits  of  a  morphologic  definition,  nor  is  it  a  special  peculiarity  of  an  or- 
gan, but  may  be  the  property  of  a  cell  as  well  as  of  a  tissue. 


62  HISTOLOGY. 

Accordingly  our  task  resolves  itself  into  :  (i)  the  study  of  the  cells 
and  of  the  tissues,  and  (2)  the  study  of  the  organs.  The  investigation 
of  cells  and  of  tissues  is  the  object  of  histology.  Histology  is  a  division  of 
minute  anatomy,  which,  because  of  the  instrument  most  used  in  its  study, 
is  called  microscopic  anatomy.  The  investigation  of  organs,  also,  so  far 
as  it  can  be  done  with  the  aid  of  the  microscope,  is  the  task  of  micro- 
scopic anatomy. 


I.   HISTOLOGY. 

(MICROSCOPIC   ANATOMY    OF   THE  CELLS  AND  THE 

TISSUES.) 

A.    THE    CELLS. 

A  cell,  ccllula,  is  a  spatially  limited  structural  element,  which  under 
certain  conditions  is  able  to  nourish  itself,  to  grow,  and  to  multiply.  In 
virtue  of  these  properties  the  cell  is  called  an  elementary  organism. 

The  cell  of  the  germ-layers  is  a  body  having  polar  differentiation, 
that  is,  free  and  basal  sides  of  the  cell  are  typically  different  (p.  60).  At 
the  free  pole  the  development  of  cuticular  formations  (p.  66),  cilia,  tactile 
hairs,  etc.,  occurs,  here  pigment  is  first  formed,  here  the  discharge  of  secre- 
tion takes  place  ;  at  the  basal  pole  processes  (fibrillae,  fibers)  originate,  by 
which  the  cell  enters  into  association  with  neighboring  tissues.*  A  line 
connecting  the  free  and  the  basal  pole  is  designated  the  chief  axis  of  the 
cell. 

The  essential  elements  of  a  cell  are  the  protoplasm  and  the  nucleus, 
and  generally,  as  third  element,  the  centrosome. 

I.  The  protoplasm,  "cell-substance,"  is  a  soft,  viscid  substance  of 
alkaline  reaction,  insoluble  in  water,  highly  distensible,  that  consists 
principally  of  albuminous  substances,  much  water  and  salts,  and  contains  a 
special  nitrogenous  proteid,  the  plastin.  In  the  protoplasm  small  granules, 
microsomes  {^plasmosomesX),  occur  in  variable  quantity;  when  numerous 
they  may  impart  to  the  protoplasm  a  dark  appearance.  They  are  irregu- 
larly distributed  ;  namely,  are  absent  in  the  superficial  layer,  the  exoplasm 
("  cuticular  stratum  "),  which  is  somewhat  denser  and  perhaps  possesses  a 
special  function.  With  the  aid  of  very  high  magnifying  powers  it  is  seen 
that   protoplasm  possesses   a   structure:  a   framework  of  fibrils  ("  filar- 

*This  polar  differentiation  can  be  demonstrated  in  many  cells  of  the  epithelial,  muscular, 
and  nervous  tissues  in  the  developed  organism  ;  in  other  cells,  particularly  in  those  of  the  sup- 
porting tissues,  insuperable  difficulties  still  exist ;  the  question  suggests  itself  whether  with  the 
differentiation  of  these  elements  from  the  germ-layers  the  polar  differentiation  was  not  lost  or 
even  whether  it  developed  at  all. 

t  "  Plasmosomes,"  in  contradistinction  to  the  granules  of  the  nucleus,  that  then  are  to  be 
named  "  karyosomes."  Specifically  developed  plasmosomes,  that  are  united  in  fibrils,  have 
been  named  "  mitochondria  "  (fibril-granules)  ;   they  are  especially  developed  in  semen-cells. 


64 


HISTOLOGY. 


mass,"  "  mitom  ")  often  forming  a  network,  which  is  embedded  in  an 
apparently  homogeneous  ground  substance  ("interfilar-ma;ss,"  "cytolinin") 
chemically  distinct  from  the  filar-mass  (Flemming).*  A  portion  of  the 
plasmosomes  he  embedded  in  the  fibrils  ;  individual  fibrils  are  nothing 
but  linear  arrangements  of  plasmosomes. 

In  many  instances  the  protoplasm  exhibits  still  other  structures  of  different 
signification,  as  follows  : 

I.  Canaliculi  of  two  kinds:  (a)  secretory  capillaries  in  gland-cells 
(P-  ^5)  j    C'^)  delicate  tubules,  that  communicate  with  the  lymph-spaces  exter- 


Achromatic 
substances 
of  the  nu- 
cleus. 


/Nuclear  membrane 


Linin. 


Centrosome. 


Inclusions. 


\  Nuclear  sap. 


Cuticular  stratum.  _ 


Filar-mass. 


Interfilar-mass. 


Chromatic 
substances 
of  the  nu- 
cleus. 


'•^■.i^"~-  L  _  Nucleolus. 


Microsomes. 


Cell  membrane  (pellicula). 


Fig.  3. — Scheme  of  a  Cell.    Microsomes  and  filar-mass  only  partly  sketched. 

nal  to  the  cell;  they  were  first  discovered  in  spinal  ganglion  cells  (Fig.  62), 
but  may  also  be  demonstrated  in  intestinal  epithelial  cells,  in  gland-cells,  in 
egg-cells,  etc.  Since  they  provide  for  the  nutrition  of  the  cells  they  have  been 
named  "  trophospongium." 

2.  Closed  networks,  that  do  not  open  at  the  periphery  of  the  cell;  this 
"  apparato  reticulare "  has  been  found  in  nerve-cells  (Fig.  63),  cartilage 
cells,  many  gland-cells,  and  in  the  corneal  endothelium.  Their  meaning  is 
still  obscure  ;  possibly  they  belong  to  the  same  category  as 

3.  Various  formed  cell-contents,  rings,  capsules,  cord-fabrics  and  the 
like. 


*  Opinions  regarding  the  structure  of  the  protoplasm  are  by  no  means  agreed.  Accord- 
ing to  Biitschli  the  structure  is  foamy,  that  is,  it  contains  small  spaces,  or  cavities,  that  do  not 
communicate  with  one  another.  A  third  theory  holds  that  the  protoplasm  is  composed  of 
granules  ("granula")  ;  the  fact  that  many  fibrils  of  the  filar-mass  consist  of  granules  aiTanged  in 
rows  has  brought  this  "  granule  theory  "  new  adherents;  on  the  other  hand,  the  teaching  of 
Altmann,  according  to  which  the  granules  are  the  true  elementary  organisms  ("  bioblasts"),  has 
been  generally  discarded. 


THE    CELLS.  65 

2.  The  nucleus  is  a  usually  vesicular,  clear,  sharply  defined  body 
lying  in  the  interior  of  the  cell,  that  consists  of  several  proteid  sub- 
stances, nuclcin  (chromatin),  paranuclciu  (pyrenin),  ///////,  nuclear  sap,  and 
aniphipyrenin.  By  their  affinity  for  stains  nuclein  and  paranuclein  are 
distinguished  from  the  other  three  so-called  achromatin  substances,  but 
differ  chemically  from  each  other.  For  example,  on  the  addition  of  dis- 
tilled water  the  structures  composed  of  nuclein  disappear,  while  those 
composed  of  paranuclein  remain  intact.  In  the  simplest  case  (in  sperma- 
tozoa) the  nucleus  is  a  compact  mass  of  nuclein,  to  which  the  paranuclein 
is  attached,  but  usually  it  consists  of  a  network  of  fine  linin  threads  and 
coarser  nuclein  cords.*  The  latter  are  of  different  caliber,  and  at  isolated 
places  are  thickened  to  knots,  the  netknots,  that  must  not  be  confused 
with  the  nucleoli.  Linin  and  nuclein  form  the  nuclear  iietwork,  the  in- 
terstices of  which   are   occupied   by  one 

Pseudopodia 

or  more  nucleoli,  consisting  of  pyrenin,  (p.  76, remark*).  Centrosome. 
and  by  the  nuclear  sap.  The  nuclear 
membrane,  not  always  present,  consists 
of  amphipyrenin  ;  often  a  membrane  is 
simulated  by  a  thin  superficial  layer  of 
nuclein.  The  nuclear  network  and  the 
nucleoli  are  subject  to  momentous 
changes,  according  to  the  age  of  the  cell. 
Most  cells  contain  but  one  nucleus  ; 
only  a  few  have  several  nuclei  (some 
wandering  cells,  giant  cells,  and  others). 
Nonnucleated  cells  (horny  cells  of  the 
epidermis,  colored   blood   corpuscles   of 

,>..,,  1    •     1      ,         Fig.  4. — Portion  of  a  Section   of  Epi- 

mammals)  ongmally  possess  nuclei,  but  thrlium  of  the  Large  intestine 

.  ,  .         ,  /-     1         1  o**'  Man.    X  ca.  660. 

lose  them  in  the  course  01  development. 

3.  The  centrosome  (central  corpuscle)  is  an  exceedingly  diminutive 
corpuscle,  that  consists  of  a  homogeneous,  less  often  honeycomb  mass, 
the  centroplasm,  and  a  very  much  minuter  corpuscle,  the  centriolef 
(centriolum).  The  centrosome  lies  in  the  protoplasm,  which  here  is  dif- 
ferentiated to  a  sometimes  clear,  sometimes  dim,  encircling  court 
("  archoplasm,"  "  idiosome") ;  sometimes  it  lies  in  the  neighborhood  of 

*  In  particularly  favorable  objects  it  can  be  seen  that  the  nuclein  cords  consist  of  rows  of 
granules,  that  lie  upon  the  linin  fibrils  ;  this  relation  is  sketched  in  the  left  half  of  the  schematic 
cell,  Fig.  3. 

f  Our  knowledge  of  the  minute  structure  of  the  centrosome  has  been  obtained  through 
the  study  of  invertebrate  animals;  the  cells  of  vertebrate  animals  are  too  small  for  investigations 
of  this  kind.      The  centriole  hns  not  yet  been  demonstrated  in  any  vertebrate  .animal  cell. 

5 


66  HISTOLOGY. 

the  nucleus  (Fig.  5),  sometimes  remote  from  this,  frequently  between  the 
free  surface  and  the  nucleus  *  (Fig.  4).  For  the  purpose  of  cell  division 
the  centrosome  passes  through  a  cycle  of  phenomena  (p.  69)  the  dura- 
tion of  which  is  very  variable  ;  the  phase  in  which  a  duplication  of  the 
centrosome,  the  "  diplosome,"  occurs  endures  the  longest,  f  For  this 
reason  the  diplosome  is  found  in  the  majority  of  resting  cells,  that  is, 
cells  not  in  the  immediate  process  of  division.^ 

An  unessential  element  of  the  cell  is  ilvQ  cell-inembrane,  an  indepen- 
dent, continuous,  membranous  border  stratum,  which  is  distinctly  marked 
off  from  the  protoplasm  ;  it  is  wanting  in  many  cells  and  when  present 
is  either  a  transformation  of  the  peripheral  zone  of  the  protoplasm  or  a 

secretory  product  of   the  latter.     When   the 
membrane  surrounds    the  cell    on    all  sides, 
X  it  is  named  pellicula;  when   it   lies    only  on 

the   free   surface,    that   is,  only    on   one  side, 
it  is   named  ciiticula.      By    crusta    is    under- 
ceiitrosome.       stood  the  dcnscr  border  zone  of  the  cell,  that 
^^°Row^oF^A°RABBn-^°>?"*?^OT'      wlthout  sharp  demarcation   gradually  passes 
IudeuI"TaXrLp'ac"e^^''''^^     into  the  protoplasm  beyond.     Other  unessen- 
tial elements  are  the  inclusions  occurring  in 
the  protoplasm  of  some  cells,  the  pigment,  glycogen,  etc.,  crystalloids, 
secretion  granules,  and  drops  of  oil,  of  aqueous  and  mucous  fluids.  § 

The  term  "paranucleus"  has  been  used  to  designate  widely  different 
formations,  the  significance  of  which  individually  is  not  yet  everywhere  deter- 
mined. Frequently  a  paranucleus  is  simulated  by  fragments  of  degenerated 
cells  that  have  been  incorporated  by  living  cells  ;  in  other  cases  the  paranucleus 
is  confused  with  the  centrosome,  with  masses  of  secretion,  or  with  the  proto- 
plasmic structures  described  on  page  64. 

*  In  many  gland-cells  the  centrosome  lies  where  the  secretion  accumulates,  the  discharge 
of  which  is  accomplished  by  contraction  of  the  protoplasmic  framework  lying  between  the  masses 
of  secretion.  In  the  cells  of  the  intestinal  epithelium  (p.  76)  provided  with  pseudopodia  the 
centrosome  lies  close  beneath  the  point  of  origin  of  the  pseudopodia ;  taking  into  account  the 
similar  behavior  of  the  ciliated  cells  of  the  epididymis  and  the  behavior  of  the  centrosome 
of  the  seminal  filaments  (cf.  The  Reproductive  Organs),  as  well  as  the  role  of  the  cen- 
trosome in  mitosis  (p.  69),  the  inference  that  the  centrosome  is  the  (active  or  passive  ?)  center  of 
motor  processes  is  highly  probable.  In  the  spermatocytes  of  ascaris  megalocephala  univalens 
and  in  carcinoma  cells  the  centrosome  has  been  observed  in  the  interior  of  the  nucleus. 

f  The  doubling  of  the  centrosome  is  preceded  by  a  division  in  two  of  the  centriole. 

\  The  diplosome  phase  is  the  most  practicable  for  estimating  the  duration  of  the  resting 
stage  of  the  cell,  because  thereby  the  competency  of  the  resting  cell  for  the  earliest  possible 
inception  of  the  mitotic  process  is  indicated. 

\  Such  products  of  metabolism,  when  they  appear  in  the  form  ot  small  particles,  may  be 
termed  "granules"  and  are  not  to  be  confused  with  the  "  plasmosomes"  (p.  63),  which  repre- 
sent structural  elements  of  the  cell.  In  practice  the  distinction  between  the  two  may  frequently 
be  involved  in  extraordinary  difficulties. 


THE    CELLS.  6/ 

Cells  differ  greatly  in  form.  They  may  be  :  spherical,  the  typical 
form  of  all  cells  in  the  embryonal  period,  while  in  the  adult,  for  example, 
resting  leucocytes  are  spherical ;  discoid,  e.  g.,  the  colored  blood  cor- 
puscles ;  polyhedral,  c.  g.,  the  liver-cells  ;  cylindrical  or  columnar,  e.  g., 
the  epithelium  of  the  small  intestine  ;  cnbical,  e.  g.,  the  epithelium  of  the 
capsule  of  the  crystalline  lens  •,flatte)icd  (so-called  squamous  epithelium), 
e.  g.,  the  epithelial  cells  of  the  blood-vessels  ;  spindle-shaped,  e.  g.,  many 
connective-tissue  cells  ;  elongated  into  fibers,  e.  g.,  smooth  muscle-fibers  ; 
stellate,  e.  g.,  many  ganglion-cells.  The  form  of  the  nucleus  usually 
corresponds  to  the  form  of  the  cell.  It  is  oval  in  cylindric,  spindle- 
shaped,  and  occasionally  also  stellate  cells  ;  rounded  in  spherical,  cubical 
and  many  stellate  cells.  Lobulated,  so-called  polymorphous  nuclei  are 
found  in  leucocytes  and  in  giant-cells  ;  they  are  an  expression  of  activity 
on  the  part  of  the  cell,  tending  to  locomotion  or  change  in  form,  or  to 
increased  metabolic  energy. 

The  size  of  cells  varies  from  forms  microscopically  small,  4  /^  * 
(colored  blood  corpuscles),  to  macroscopic  bodies  (eggs  of  birds,  of  am- 

0  /^         1        s  2)^ 


^   ^.-^        '^ 


^ 


sA  JO'  8  iO  Minutes. 

Fig.  6.— Leucocytes  of  a  Frog.    X  560.    Changes  in  form  observed  during  ten  minutes  ;  o,  at  the  begin- 
ning of  the  observation  ;  ^,  a  half  minute  later,  etc.    Technic  No.  49. 

phibians).  The  size  of  the  nucleus  corresponds  in  general  to  that  of  the 
protoplasmic  body  ;  only  mature  ova,  despite  their  great  dimensions, 
have  tiny  nuclei. 

In  some  instances  the  cells  unite  in  a  syncytium,  that  is,  a  common 
protoplasmic  mass,  in  which  occasionally  the  scattered  nuclei  still  indi- 
cate the  otherwise  undefinable  cell  territories. 

The  vital  properties  of  cells  will  be  discussed  here  only  in  so  far  as 
they  can  be  studied  by  direct  microscopic  observation  ;  other  details 
must  be  sought  in  textbooks  of  physiology.  Accordingly,  the  phe- 
nomena of  motion  in  cells,  the  reproduction  of  cells,  and  those  micro- 
scopic processes  which  are  associated  with  the  secretory  activity  of  cells 
will  be  considered. 

*  A  micron,  ixiKpov  =  //  =  o.ooi  mm. 


68  HISTOLOGY. 

The  plienomcna  of  motion  occur  in  the  form  of  ameboid*  activity,  of 
cihary  movement,  and  of  contraction  of  certain  fibers  (muscle-fibers). 
The  ameboid  motion  is  the  most  important ;  of  wide-spread  occurrence, 
it  has  been  observed  in  nearly  all  the  cells  of  the  animal  body.  In  well- 
marked  cases,  e.  g.,  in  leucocytes,  the  protoplasm  of  the  cell  projects 
finer  or  coarser  processes  (pseudopodia),  that  divide  and  flow  together 
again  and  in  this  way  produce  the  greatest  variety  of  forms.  These 
processes  may  be  retracted  or  they  may  become  attached  somewhere 
and  partially  draw  the  remainder  of  the  cell-body  after  them,  the 
result  of  which  is  locomotion,  or  the  so-called  "wandering"  of  cells. 
The  wandering  cells  play  an  important  part  in  the  economy  of  the  animal 
body.  The  processes  can  flow  around  granules  and  cells  and  thus 
enclose  them  in  the  cell-body,  an  occurrence  described  as  Xh^  feeding  of 
the  cell.f  Cells  that  can  transform  or  "digest"  such  inclusions  are 
named  phagocytes.  Ameboid  movements  take  place  very  slowly,  in 
warm-blooded  animals  only  on  artificial  warming  of  the  object.  For 
ciliary  motion  and  the  phenomena  of  contraction,  see  the  chapters  on 
epithelial  and  on  muscle  tissue,  respectively. 

There  is  another  phenomenon  of  motion,  which,  however,  does  not 
occur  in  the  living  cell.  This  is  the  so-called  moleailar  motion,  an  oscil- 
lation of  minute  granules  in  the  cell,  the  result  of  molecular  currents  in 
the  fluid  in  which  they  are  suspended.  It  may  often  be  observed  in  the 
salivary  corpuscles  (see  the  Lymph-follicles  of  the  Tongue). 

Reprodiictioji  and  Midtiplication  of  Cells. — Formerly,  two  kinds  of 
cell  formation  were  distinguished,  spontaneous  generation  {^generatio 
cBqidvocd)  and  generation  by  division.  According  to  the  theory  of  spon- 
taneous generation,  cells  were  supposed  to  originate  in  a  suitable  fluid, 
the  cytoblastema.  Something  of  this  kind  may  formerly,  in  unthinkably 
early  ages,  have  occurred  ;  but  now  we  recognize  only  one  kind  of  cell 
generation,  that  is,  reproduction  by  division  of  preexisting  cells.  "  Omnis 
cellula  e  cellula."| 

In  the  division  of  a  cell,  first  the  nucleus  and  then  the  protoplasm 
divides  into  two  usually  equal  parts.     In  this  process  a  special  grouping 

*This  movement  is  exhibited  in  its  perfection  by  unicellular  organisms  named  amebse; 
thence  the  phrase  "  ameboid  motion." 

f  This  must  not  be  confused  with  the  nutrition  of  the  cell,  which  is  effected  by  a  series 
of  complicated  chemical  processes  within  the  cell ;  diosmotic  currents,  imbibition,  molecular 
pressure,  etc. 

j  Likewise,  a  new  nucleus  can  arise  only  by  the  division  of  an  existing  nucleus.  The 
theory  of  spontaneous  generation  of  nuclei,  according  to  which  nuclei  originate  directly  from 
the  protoplasm  and  independently  of  existing  nuclei,  lacks  unequivocal  evidence. 


THE    CELLS. 


69 


and  rearranging  of  the  nuclear  substances  (p.  65)  take  place  according 
to  definite  laws.  This  mode  of  division  is  called  indirect  division,  division 
by  mitosis,^  karyokiiicsis.  Its  cycle  is  usually  divided  into  three  phases, 
as  follows  : 

(i)   Prophase. 

The  centrosome  and  the  nucleus  approach  each  other  and  finally 
the  former  arrives  in  the  immediate  neighborhood  of  the  nuclear  mem- 
brane, surrounded  by  the  bright  halo  (p.  65),  in  which  the  radiating, 
delicate  fibrils  now  become  more  distinct ;  collectively  these  fibrils  are 
called  astrospJicre.  The  centrosomes,  previously  duplicated  in  the  rest- 
ing state  of  the  cell  (p.  66),  now  move  apart  and  instead  of  the  single 
astrosphere  enveloping  the   diplosomes   there  are  two  present,  one  for 


Central  spindle. 


Chromosomes. 


Centrosome. 


Fig.  7.— Scheme  of  the  Close  Coi 


Fig.  S.— Scheme  of  the  Loose  Coil. 


each  centrosome  (Fig.  7).  Then  the  nucleus  enlarges,  the  nuclear  net- 
work becomes  richer  in  chromatin,  and  its  nuclein  cords  soon  appear  in 
the  form  of  convoluted  segments!  (chromosomes),  that  are  placed 
transversely  to  the  long  axis  of  the  nucleus.     The  number  of  the  chro- 


*  ulrnc,  the  thread,  because  in  this  process  threads  are  visible  in  the  nucleus.  There  is  a 
second  mode  of  division,  in  which  the  nuclei  divide  simply  by  constriction,  without  the  occur- 
rence of  a  regular  grouping  of  the  nuclear  structures.  This  is  called  direct  or  amitotic  division. 
However,  it  is  very  probable  that  this  kind  of  division  in  vertebrates,  under  normal  conditions, 
has  not  the  significance  of  a  physiologic  reproduction  and  multiplication  of  cells,  but  occurs 
only  in  cells  which  are  degenerating — for  very  often  the  division  of  the  protoplasm  does  not 
follow,  so  that  only  a  multiplication  of  nuclei  takes  place.  This  frequently  happens  in  leuco- 
cytes, also  in  epithelial  cells — e.  g.,  in  the  superficial  epithelial  cells  of  the  urinary  bladder  of 
young  animals. 

f  These  segments  are  present  in  many  resting  nuclei,  but  owing  to  the  numerous  lateral 
branches,  by  which  they  unite  with  their  neighbors  in  a  network,  they  are  not  easily  distin- 
guished. At  the  beginning  of  division  the  lateral  branches  are  drawn  in,  whereby  the  segments 
become  thicker  and  appear  more  distinct.  In  other  nuclei  the  chromatin  is  disposed  in  a 
single  thread,  that  later  divides  transversely  into  chromosomes. 


70 


HISTOLOGY. 


mosomes  is  constant  for  each  animal  species,  in  man  probably  twenty- 
four. 

The  form  of  the  chromosomes  is  usually  that  of  a  loop.  The  closed 
ends  are  directed  toward  the  centrosomes,  the  polar  side  or  polar  field, 
the  free  ends  toward  the  opposite  pole  of  the  cell.  In  this  stage  the 
chromosomes  form  a  close  coil  (Fig.  7) ;  but  they  soon  grow  thicker 
and  less  tortuous,  thereby  converting  the  close  coil  into  the  loose 
coil  (Fig.  8).  In  the  latter  the  curves  of  some  of  the  loops  can  be 
detected  pointing  toward  the  opposite  pole  [cf.  Fig.  14). 

Meanwhile  the  two  centrosomes,  increasing  mainly  at  the  circum- 
ference, move  apart  and  wander  along  the  nuclear  membrane,  each 
to  a  point  90°  distant  from  its  original  position.  Between  the  retreating 
centrosomes  a  span  of  delicate  fibers  appears,  which  form  the  central 
spindle,  to  which  fibers  of  the  astrospheres  become  attached  and  can  now 
be  traced  to  the  chromosomes.      Toward  the   completion  of   the  pro- 


Polar  radiation. 


Nuclear  spindle. 


Fig.  9.— Scheme  of  the  Mother  Star. 


Fig.  10. — Scheme  of  Metakinesis. 


phase  the  nuclear  membrane  vanishes  and  the  nucleolus  becomes 
invisible. 

(2)  Metaphase. 

The  centrosomes  have  reached  diametrically  opposite  points,* 
their  fibrils,  with  which  perhaps  parts  of  the  nuclear  membrane  are 
associated,  extend  to  the  chromosomes  and  now  appear  in  the  figure  of 
a  spindle,  the  nnclear  spindle,  at  each  apex  of  which  lies  a  relatively 
very  large  centrosome  encircled  by  the  astrosphere,  which  in  this  stage 
is  also  known  as  the  "  polar  radiation. "f     The  chromatin  loops  move 


*  Up  to  this  point  this  description  of  the  behavior  of  the  centrosome  is  not  invariably 
applicable  ;  for  example,  in  ascaris  megalocephala  univalens  the  centrosome  divides  in  the  in- 
terior of  the  nucleus,  which  elongates  and  allows  a  centrosome  to  emerge  at  each  end.  With 
their  exit  the  nuclear  spindle  is  formed.      In  succeeding  events  the  processes  are  identical. 

•f  Remains  of  the  central-spindle  still  lie  in  the  axis  of  the  nuclear-spindle. 


THE    CELLS. 


71 


to  the  equator  of  the  spindle,  in  the  future  plane  of  division  of  the 
nucleus,  and  are  soon  arranged  so  that  their  closed  ends  are  directed 
toward  the  axis  of  the  spindle,  their  free  ends  toward  the  equator  (Fig. 
9).  Viewed  from  an  apex  of  the  spindle  this  grouping  of  the  segments 
has  the  appearance  of  a  star,  the  viotJier  star  (monaster). 

During  the  formation  of  the  mother  star,  often  earlier,  in  the  first 
stages  of  the  prophase,  the  chromatin  loops  divide  longitudinally,  so  that 
each  single  loop  forms  two  sister  loops.  This  is  followed  by  division  of 
the  nucleus  exactly  into  halves,  while  by  the  contraction  of  the  spindle 
fibers  (?)  the  one  sister  loop  is  drawn  to  one  pole,  the  other  sister  loop  to 
the  other  pole  of  the  nuclear  spindle.  This  process  is  named  nieta- 
kinesis  (Fig.  10) ;  it  is  involved  in  a  separation  of  the  centrosomes  from 
each  oth^r.      In  this  stage  the  nuclear  segments  appear  in  the  figure  of 


Fig.  II. — Scheme  of  the  Daughthr  Stars. 


Fig.  12.— Scheme  of  Cell  Division. 


two  daughter  stars,  they  form  the  dyastcr.  Each  daughter  star  exhibits 
polarity  (Fig.  1 1). 

(3)  Anaphase. 

These  relations  are  soon  obliterated,  inasmuch  as  the  centrosome 
diminishes  again,  then  duplicates  itself,  and  the  chromosomes  thrust  out 
lateral  twigs  for  anastomosis  with  neighbor  chromosomes  and  so  repro- 
duce the  fabric  of  the  resting  nucleus.  While  the  spindle  and  the  greater 
portion  of  the  polar  radiation  become  invisible,  and  a  new  nuclear  mem- 
brane appears,  beginning  opposite  the  "  polar  side,"  the  nucleus  swells  by 
imbibition  of  nuclear  sap,  becomes  spherical,  and  nucleoli  appear;  at  the 
same  time,  at  the  equator  of  the  cell,  a  division  of  the  hitherto  quiescent 
protoplasm  begins  (Fig.  12),  which  leads  to  complete  separation  into 
halves. 

In  rare  cases,  especially  in  those  of  a  pathologic  nature,  the  nucleus 
simultaneously  divides  in  the  mode  of  mitosis  into  more  than  two  nuclei. 

The  duration  of  cell   division,  in  which   the   progress   of  the   indi- 


72  HISTOLOGY. 

vidual  stages  is  not  equally  rapid,  varies  from  a  half  hour  (in  man)  *  to 
five  hours  (in  amphibia). 

Special  modifications  of  cell  division  are  the  so-called  endogenous 
cell  formation  and  budding.  The  endogenous  cell  formation  occurs  in 
cells  that  possess  a  firm  envelop  (egg-cells,  cartilage  cells).  The  process 
of  division  is  precisely  the  same  as  that  previously  described,  except  that 
all  the  descendants  of  one  cell  (mother  cell)  arising  by  successive  divi- 
sions (daughter  and  grand-daughter  cells)  remain  inclosed  in  the 
common  capsule  (Fig.  44).  Gemmation  or  budding  indicates  a  kind  of 
division  in  which  the  products  are  of  unequal  size,  or  in  which  the  cell 
develops  processes  that  are  set  free  by  constriction  and  become  inde- 
pendent cells  (see  bone  marrow). 

The  young  cells  always  resemble  in  character  the  mother-cells. 
Such  a  case  as  connective-tissue  cells  arising  from  the  division  of  an  epi- 
thelial cell  never  occurs  [cf.  also  p.  61). 

The  phenomena  of  secretion. — (See  Secretory  Activity  of  Epithelial 
Tissue. j 

The  duration  of  life  in  nearly  all  cells  is  brief;  the  old  elements  dis- 
integrate, new  ones  appear  in  their  places.  Dying  cells  are  character- 
ized by  decrease  in  the  volume  of  both  nucleus  and  protoplasm.  The 
latter  often  seems  to  have  an  indented  border  or  it  stains  more  deeply, 
while  the  chromatin  substance  of  the  nucleus  either  diminishes  or  ap- 
pears in  the  form  of  fragments  that  stain  homogeneously.  Vacuoles  in 
the  protoplasm  or  in  the  nucleus  are  signs  of  dying  cells.  Dying  cells  in 
abundance  may  be  observed  in  epithelia,  where  formerly  they  were  often 
regarded  as  peculiar  kinds  of  cells  [cf.  also  Fig.  26). 

The  groivth  of  cells  preeminently  concerns  the  protoplasm  and  only 
exceptionally  takes  place  equally  in  all  directions,  in  which  case  the 
original  form  of  the  cell  is  retained  {e.  g.,  egg-cell)  ;  as  a  rule,  an  un- 
equal growth  occurs.  As  a  result  of  unequal  growth  the  original  form 
is  altered  ;  the  cell  becomes  elongated,  or  flattened,  or  branched,  etc. 
The  majority  of  cells  are  soft  and  susceptible  to  change  in  form  from 
mechanical  influences  ;  as,  for  example,  the  cylindric  epithelial  cells  in 
the  empty  urinary  bladder,  which  in  the  filled  organ  are  low,  flattened 
structures  ;  or,  the  epithelial  cells  of  the  peritoneum,  which  by  distention 
acquire  three  times  their  former  superficies. 

Secretory  products  of  cells. — The  secreted  materials  are  either  wholly 
removed  (as  most  glandular  secretions)  or  they  become  rigid  and  remain 


*  The  disappearance  of  the  mitotic  figures  in  the  human  cadaver  is  not  complete  until 
after  an  elapse  of  forty-eight  hours. 


THE    CELLS.  73 

in  contact  with  tl.e  cells.  To  the  latter  belong  certain  intercellular  sub- 
stances ;  many  of  these  are  a  secretion  of  cells,  others  are  produced  by  a 
transformation  of  the  peripheral  layers  of  the  cell  protoplasm,  still  others, 
by  complete  metamorphosis  of  the  cells  (some  cells  undergo  degener- 
ation in  the  development  of  the  intercellular  substance).  It  is  very  dif- 
ficult to  distinguish  whether  individual  intercellular  substances  were 
formed  by  the  one  process  or  the  other ;  many  points  in  this  matter  are 
still  the  subject  of  lively  controversy. 

The  intercellular  substances  occur  either  in  small  amount,  as  struc- 
tureless, soft,  perhaps  fluid,  ceinoit-substance,  between  epithelial  cells, 
connective-tissue  cells,  smooth  muscle-fibers,  etc.  ;  or  in  large  amounts, 
exceeding  the  mass  of  the  cells,  and  then  are  called  ground-substance. 
The  ground-substances  are  either  formless  (homogeneous)  or  formed  ;  in 
the  latter  case  they  are  for  the  most  part  transformed  into  fibers  or 
granules  of  different  nature.  The  scanty  remnants  of  formless  substance 
found  between  the  fibers  or  granules  also  are  called  cement-substance. 

Union  of  cells. — Cells  unite  with  one  another  either  by  contact 
(union  by  contiguity)  or  they  extend  into  one  another  by  means  of 
shorter  or  longer  processes  (union  by  continuity).  Such  processes  may 
possess  delicate  fibers,  or  fibrillse,  that  extend  through  several  cells,  as 
for  example,  in  stratified  squamous  epithelium  and  in  the  elements  of 
nerv^e  tissue.  The  independence,  the  possibility  of  territorial  isolation  of 
the  individual  cells  is  not  impaired  thereb}'.  In  other  cases,  however, 
cells  originally  distinct  fuse  into  a  common  protoplasmic  mass,  a  syncy- 
tium, in  which  then  only  the  nuclei,  often  stationed  at  very  irregular 
intervals,  occasionally  indicate  the  individual  cell  territories.  The  inde- 
pendence of  the  cells  is  thereby  more  or  less  sacrificed. 

TECHNIC. 

Xo.  I. — For  the  study  of  nuclear  structure  and  karyokinesis  am- 
phibian larvae  are  most  suitable.  Those  most  readily  procured  are  the 
larvae  of  the  water-salamander,  which  in  the  months  of  June  and  July 
abound  in  every  pool.  Place /;r.sVi;/r  caught  specimens,  3  to  4  cm.  long, 
in  about  100  c.c.  of  chromic-acetic  acid  (p.  32).  After  three  hours 
place  the  larvae  in  running  water  for  eight  hours  and  then  in  70  per  cent, 
alcohol.  At  the  expiration  of  four  hours,  or  later,  the  objects  are  ready 
for  further  treatment. 

(a)  Xuclear structure. — With  a  scalpel  carefully  scrape  the  epithe- 
lium from  the  skin  of  the  abdomen,  with  two  pairs  of  fine  forceps  strip 
off  the  thin  corium,  stain  it  for  from  one  to  three  minutes  in  5  c.c.  of 
Hansen's  hematoxylin  (p.  38),  and  mount  in  xylol-balsam  (p.  50).  Be- 
tween the  round  glands  beautiful  connective-tissue  cells  with  large  nuclei 
may  be  seen.      The  fibrillar  structure  of  the  protoplasm,  the  centrosome, 

k 


74 


HISTOLOGY. 


Protoplasm. 


Nucleus.  — ^•'> 


Nuclear  membrane. 
Nuclear  network. 
Nucleoli. 


the  astrosphere,  and  the  finer  structures  of  the  nucleus  can  be  recognized 
only  by  the  employment  of  complicated  methods  and  the  highest  mag- 
nification.     The    results   obtained   by 
ordinary  methods  are  like  those  pic- 
tured in  figure  13. 

The  cross-striped  muscles  of  the 
tail  and  the  membranes  of  smooth 
muscle-fibers  (the  latter  may  be  read- 
ily obtained  by  stripping  off  the  mus- 
cularis  of  the  intestine)  also  furnish 
beautiful  slides. 

{b)    Karyokinesis. — With    a    pair 
of  fine  scissors  cut  round  the  margin 
of  the  cornea  and  strip  off  the  same  ; 
stain  and  preserve  like  a.     The  prep- 
aration must  be  placed   on  the  slide 
with   the  convex  surface  of  the  cor- 
nea upward  ;  in  the  epithelium,  even 
with  the  low-power  objective,  many  karyomitotic  figures  may  be  seen, 
which  are  revealed  by  their  intense  color  ;  with   stronger  magnification 
pictures  such  as  are  represented  in  figure  \a^  can  be  seen.      By  this  method 


Fig.   13.— Connective-tissue  Cell    from 

THE     CORIUM     OF     TrITON     T^NIATUS. 

Surface  \'iEW.  X  560.  Only  the  coarser 
filaments  of  the  nuclear  network  can  be 
distinctly  seen  ;  with  this  magnification 
the  finer  filaments  appear  as  minute  dots, 
the  nucleoli  as  parts  of  the  nuclear  net- 
work. 


Close  coil 
(viewed  from 
the  side). 
Polar  side. 


\ 


Loose  coil  (viewed 
from  above — i.e.^  from 

the  pole).  Mother  star  (viewed  from  the  side). 


m 


w^r-^^ 


Polar 
radiation. 


Spindle 


Mother  star  (viewed 
from  above). 


Daughter  stars. 


Beginning,  Completed, 

Division  of  the  protoplasm. 


Fig.  14. 


-Karvokinetic  Figures  from  a  Surface  Preparation  of  the  Epithelium  of  the  Oral 
Cavity  of  Triton  Alpestkis.    X  560. 


the  nuclear  spindle  and  the  polar  radiation  can  be  perceived  only  in  espe- 
cially favorable  preparations — c.  g.,  eggs  of  siredon  and  of  trout. 

The  centrosomes  and  first  stages  of  spindle  formation  can  only  be 
seen  with  immersion  lenses  and  in  preparations  made  after  technic  No.  3 
(p.  88). 


THE     TISSUES. 


75 


The  delicate  lamelL-e  suspended  from  the  convex  side  of  the 
cartilaginous  gill-arch,  as  well  as  the  epithelium  of  the  floor  of  the  oral 
cavity,  are  highly  suitable  objects.  Occasionally  not  a  single  karyo- 
kinetic  figure  is  found.  Isolated  figures  may  sometimes  be  observed  in 
preparation  a. 

B.    THE    TISSUES. 

I.    THE    EPITHELIAL   TISSUES. 

The  elements  of  epithelial  tissue,  the  epithelial  cells,  are  sharply 
defined  cells  consisting  of  protoplasm  and  nucleus.  A  cell  membrane  is 
frequently  absent,  often  only  a  crusta  is  present  (p.  66).  The  majority 
of  epithelial  cells  are  soft  and  plastic,  yield  readily  to  the  pressure  of 
surrounding  elements,  the  result  of  which  is  great  diversity  of  outline. 
In  general   two  principal  forms   can  be   distinguished:  they?^'?/ and  the 


ii^r 


Fig.  15.— Isolated  Epithelial  Cells  OF  THE  Rabbit.  X  560.  i.  Squamous  cells  (mucous  membrane 
of  mouth).  Technic  No.  96.  2.  Cylinder  cells  (corneal  epithelium).  3.  Cylinder  cells,  with  cuticu- 
las,  J  (intestinal  epithelium).    4.  Ciliated  cells;   A,  cilia  (bronchial  epithelium).     Technic  on  page  29, 

cylindrical  (better,  prismatic).  These  extremes  are  united  by  numerous 
transitional  forms. 

The  flat  epithelial  cells,  squamoits  epithelial  cells,  pavement  epithelial 
rifZ/j-,  rarely  are  symmetrical  in  form,  excepting  the  pigmented  epithelium 
of  the  retina,  which  consists  of  tolerably  regular  hexagonal  cells  (Fig.  i6)  ; 
generally  the  contour  is  very  irregular. 

The  cylindrical  epithelial  cells,  cylinder  cells,  seen  from  the  side  are 
elongated  elements,  the  height  of  which  considerably  exceeds  the 
breadth  ;  seen  from  above  they  appear  hexagonal  ;  therefore  they  are  in 
reality  prismatic. 

Cells  that  are  as  high  as  they  are  broad  are  called  cubical  epithelial 
cells.* 

Many  cylinder  cells    have   a  sometimes    homogeneous,   sometimes 


*  Such  cells  are  frequently  also  called  pavement  cells. 


76 


HISTOLOGY. 


striated  border  on  their  free  upper  surface  *  (Fig.  15,  3  i')  ;  it  is  a  cutic- 
ula.  Other  cylinder  cells  are  beset  with  delicate  filamentous  processes  f 
(cilia)  on  their  free  surface,  that  during  life  are  in  constant  active  vibration 
to  and  fro  in  a  definite  direction.     These  are  called  ciliated  cells. 

The  specially  differentiated  sensory  or  ncuro- epithelial  cells  will  be 
described  in  connection  with  the  organs  of  special  sense. 

Continuous  layers  of  epithelial  cells,  which  cover  outer  and  inner 
surfaces  of  the  body,  are  called  "epithelia."  The  epithelia  are  some- 
times composed  of  a  single  stratum,  sometimes  of  several  strata,  and 
accordingly  the  following  varieties  are  distinguished  : 

I.  Simple  (one-layered)  sqiiarnons  epithelium  (Fig.  16)  :  in  the 
pigmented  layer  of  the  retina,  the  alveoli  of  the  lungs,  the  pericar- 
dium,   the    pleura,    the    peritoneum,  the    rete    testis,    the    membranous 


'■<,') 


Fig.  16. — Pigmented  Epithelium  of  the  Retina 
OF  Man.  Viewed  from  the  surface.  X  560. 
Technic  No.  180. 


3  — 


«^       — 


fp- 


Fig.  17. — Simple  Cylinder  Epithelium  of  the 
Small  Intestine  OF  Man.  X  560.  c.  Striated 
culicular  border.  2-.  Cylinder  cell.  //.Tunica 
propria.     Techniclike  No.  no. 


Fig.  18. — Stratified  Squamous  Epithelium  of 
THE  Larynx  of  Man.  X  240.  i.  Cylinder 
cells.  2.  Polygonal  cells.  3.  Squamous  cells. 
Technic  No.  128. 


labyrinth,    also    the   epithelium   of    the    articular    cavities,    of   the   ten- 
don    sheaths,    of    the  endocardium,    the    blood-    and    lymph-vessels. | 


*The  strije  are  the  boundaries  of  minute  rods  (Fig.  17,  c)  that  occasionally  can  be  dis- 
tinctly seen  even  with  medium  magnification ;  between  them  processes  of  the  protoplasm, 
"  pseudopodia,"  the  length  of  which  often  varies  greatly,  can  extend  toward  the  free  surface. 
Such  pseudopodia  can  be  seen  also  on  the  epithelial  cells  of  the  human  large  intestine  (Fig.  4). 
The  socalled  brushborder  of  the  renal  epithelium  is  likewise  constructed  of  minute  rods,  that 
differ  from  similar  formations  only  in  their  greater  delicacy  ;  whether  this  border  belongs  to  the 
cuticular  formations  is  questionable,  for  the  assumed  constancy  of  the  structure  is  disputed  (see 
the  chapter  on  the  kidneys). 

t  Very  high  magnifications  show  that  each  cilium  is  in  relation  with  a  granule,  the  "  basal 
corpuscle,"  lying  close  to  the  free  surface,  which  perhaps  is  the  center  of  motion  for  the  cilium. 

J  The  last-named  five  epithelia  are  also  called  eiidothelia,  their  elements,  endothelial  cells. 
In  normal  anatomy  these  names  are  superfluous.  It  has  recently  been  suggested  to  designate 
at  least  the  epithelium  of  the  blood-  and  lymph-vessels  as  endothelium. 


THE     TISSUES. 


77 


With  these  is  enumerated  the  epithehum  formed  of  a  single  layer  of 
cubical  cells,  occurring  in  the  plexus  chorioidei,  on  the  inner  surface  of 
the  capsule  of  the  lens,  in  the  thyroid  gland,  and  in  the  majority  of  other 
glands. 

2.  Simple  cylvidcr  epithelium  (Fig.  17)  :  in  the  intestinal  canal  and 
in  the  ducts  of  many  glands. 

3.  Simple  ciliated  epithelium  (Fig.  i^,  4)'.  in  the  smallest  bronchi, 
in  the  uterus  and  oviducts,  in  the  accessory  spaces  of  the  nasal  fossae,  in 
the  central  canal  of  the  spinal  cord. 

4.  Stratified  (many-layered)  squamous  epithelium  (Fig.  18)  :  not  all 
the  elements  of  this  variety  are  squamous  cells  ;  the  lowermost  stratum 
is  composed  of  cylinder  cells  ;  superposed  on  this  are  several  strata  of 
very  differently  shaped  cells,  mainly  ir- 
regularly polygonal,  over  which  lie 
successive  strata  of  cells  that,  as  they  ap- 
proach the  surface,  become  progres- 
sively thinner  and  flatter.  The  strati- 
fied squamous  epithelium  occurs  in  the 
mouth,  in  the  pharynx,  in  the  esophagus, 
on  the  vocal  cords,  on  the  ocular  con- 
junctiva, in  the  vagina,  and  in  the  female 
urethra.  The  epidermis  also  consists  of 
a  stratified  squamous  epithelium,  which 
is  characterized  by  the  cornification  of 
the  cells  of  the  superficial  strata,  which 
are  transformed  into  horn}'  scales  with- 
out nuclei.  Cornified  cells  are  also  found  on  the  hairs  and  nails,  but  in 
these  situations  they  are  nucleated. 

Stratified  cylindric  and  stratified  ciliated  epithelium  are  also  recog- 
nized, although  it  has  been  shown,  particularly  in  sections,  that  this 
stratification  is  simulated  by  the  arrangement  of  the  nuclei  of  the  cells 
at  different  levels  in  several  transverse  rows  ;  the  cells  themselves  all 
rest  upon  the  connective-tissue  base,  but  do  not  all  extend  to  the  free 
surface  (Fig.  19).  Such  epithelium  is  accordingly  one-layered  and  is 
distinguished  from  the  ordinary  "simple"  epithelium,  in  which  the 
nuclei  stand  \n  o)ie  row — "single  row" — as  ;//<?// r-r^ZiYv/ (multi-lineal) 
epithelium.  Doubtless  the  majority  of  the  stratified  cylinder  and  ciliated 
epithelia  hitherto  described  are  merely  "many-rowed."  Accordingly  we 
recognize  the  following  : 

5.  Stj'atijied  {possxhXy  many-rowed)  cylinder  epithelium:  in  man  is 
found  onl\-  on  the  conjunctiva  palpebrarum,  in  the  main  excretory  ducts 


Fig.  19. — Scheme  of  a  Manv-rowed 
Epithelium. 


78 


HISTOLOGY. 


w 


of  certain  crlands,  and  in  a  division  of  the  male   urethra.      The  arrange- 
ment  of  the  strata  is  similar  to  that  of — 

6.    Stj'atified  ciliated  epithelium  :    only  the 
r  '  i  most  superficial  cells  are  cylindric  and  carry  cilia  ; 

3-;^  I  in  the  deepest  layers  the   elements  are  mainly 

l"^'  '' h  spherical,   in   the   middle   layers   spindle-shaped 

gJf  ^'  (Fig-  2o).      Stratified  ciliated  epithelium  is  said 

I  y  to  occur  in  the  larynx,  in   the   upper  portion  of 

the  pharynx,  and  in  the  eustachian  tube ;  prob- 
ably it  is  only  many-rowed,  like  the  epithelium 
of  the  nasal  fossae,  the  trachea,  the  large  bronchi, 
and  the  epididymis,  in  which  all  cells  actually 
reach  to  the  connective  tissue. 

Between  the  epithelial  cells  extremely  nar- 
row clefts  often  occur,  intercellular  spaces,  which 
are  occupied  by  a  frequently  very  scanty,  soft,  perhaps  fluid,  intercellular 
substance.^     In  many  epithelia  (in  the  cylinder  epithelia  of  the  mucous 


Fig.  20. — Many-rowed  Cili- 
ated Epithelium.  X  560. 
From  the  respiratory  nasal 
mucous  membrane  of  man. 
I.  Oval  cells.  2.  Spindle- 
shaped  cells.  3.  Cylinder 
cells.  4.  Connective  tissue. 
Technic  No.  200. 


Cuticula 


Cross-section 
of  a 
terminal  bar. 


Fig.  21. — Cylinder  Epithelium  of  an  Intes- 
tinal Villus  of  Man.  Magnified  about  600 
times.  Network  of  terminal  bars  :  A,  view  of 
free  surface  ;  B,  lateral  aspect ;  on  the  left  the 
cross-sections,  on  the  right  the  lateral  surfaces 
of  the  terminal  bars  are  seen.     Technic  No.  3. 


Network  of 
terminal 
bars. 


Cuticula. 


Intercellular    y 
substance. 


Fig.  22.— Scheme  of  the  Network  of  Terminal 
Bars.  The  two  cells  on  the  left  are  divided 
lengthwise  into  halves;  the  two  on  the  right 
are  drawn  as  complete  cylinders  or  prisms. 


membranes  and  in  the  majority  of  the  glandular  epithelia,  also  in  the 
stratified  epithelium  of  the  mucous  membrane  of  the  tongue  and  in  the 
transitional  epithelium  of  the  urinary  organs)  the  intercellular  spaces  are 


*  Because  in  the  human  skin  these  intercellular  spaces  have  been  successfully  injected 
through  the  lymph-vessels,  it  was  believed  that  this  substance  is  identical  with  ordinary  lymph. 
However,  this  is  not  correct,  for  the  intercellular  substance  of  epithelium  reacts  differently  ;  it 
becomes  black  when  treated  with  silver  nitrate. 


THE     TISSUES. 


79 


closed  toward  the  free  surface  by  very  delicate  bars  of  a  peculiar  cement- 
substance  ;  since  these  bars,  ''terminal  bars''  [Schlnss/cisten),  are  con- 
nected with  one  another  they  form  a  "  network  of  terminal  bars  "  [Sehlnss- 
leistennetz),  in  the  meshes  of  which  the  ends  of  the  epithelial  cells  directed 
toward  the  free  surface  are  inserted. 

The  union  of  the  epithelial  cells  is  effected  in  such  a  manner  that 
either  they  present  smooth  surfaces  of  contact  to  one  another, — namely  by 
the  intervention  of  intercellular  substance, — or  they  interlock  by  variously 
shaped  processes,  the  latter  being  pressure-effects.  The  delicate  spines 
and  thorns  visible  on  the  surfaces  of  many  epithelial  cells  have  been 
regarded  as  similar  processes.  But  these  are  connecting  bridges,*  often 
cord-  and  net-like,  which  pierce  the  intercellular  substance  and  establish 
an  intimate  union  v/ith  neighbor  epithelial  cells.  Cells  provided  with  such 
thorns  and  ridges  are  called  prickle-cells  ;  the  processes  are  aptly  desig- 
nated by  the  appropriate  name  of  intercellular 
bridges  (Fig.  23).     They  were  first  seen  on  the  _..^^ 

poh'gonal    cells   of  stratified   squamous   epithe-  ,  ,^^- 

lium.t  but  they  also  occur  on  the  cells  of  simple  '-;' 

squamous  and  simple  cylinder  epithelium, — for 
example,  of  the  stomach  and  of  the  intestines, —  '"'w-^.^o-f^y 

but  there  they  are  extremely  delicate  and  can  be      fig.  23.— from  a  Vertical 

,'         ,  ,  ....  .    ,  Section  OF  THE  Stratum 

demonstrated  only  by  the  application  ol  special  germinativum    of    the 

Epidermis.    >,  560.    Seven 

methods.     The  length  of  the  intercellular  bridges    .      squamous  epithelial  ceiis 

^  ^  united       by      intercellular 

and  the  diameter  of  the  "  intercellular  clefts  "  oc-  bridges,   xechnic  like  No. 

89. 

curring  between  them  vary  greatly  in  the  differ- 
ent forms  of  epithelium  and  in  the  different  physiologic  states  of  the  tissue.  | 
Epithelium  possesses  no  blood- §  and  lymph-vessels,  but  nerves  are 
found  in  some  situations,  for  example,  in  the  epithelium  of  the  skin  and 
of  many  mucous  membranes. 

*  These  bridges  contain  fibrils,  that  can  be  traced  in  the  interior  of  the  cells  (the  filar- 
mass,  p.  63),  and  are  the  ground  on  which  such  epithelium  was  said  to  have  a  "  fibrillar"  struc- 
ture, a  description  that  can  only  lead  to  perplexity,  because,  for  example,  it  tends  to  produce 
confusion  with  the  fibrillar  structure  of  connective  tissue,  which  is  something  wholly  different. 

f  The  basal  surfaces  of  the  cylinder  cells  of  stratified  squamous  epithelium  are  also  pro- 
vided with  short  processes,  directed  toward  the  subjacent  connective  tissue,  the  "rivet-fibers" 
(^Haftfasern),  that  can  be  made  visible  only  by  means  of  complicated  methods. 

i  In  fresh,  living  tissues  (e.  g.,  in  the  tail  of  amphibian  larvje)  the  intercellular  spaces 
can  scarcely  be  seen,  but  in  certain  conditions  dependent  on  disturbance  of  the  circulation  of 
lymph  become  more  distinct.  Then  the  intercellular  spaces  appear  as  tiny  vacuoles  in  the 
hyaline  border  stratum  of  each  epithelial  cell.  The  thicker  the  stratified  epithelium  is,  the  wider 
are  the  intercellular  spaces,  the  longer  are  the  intercellular  bridges  ;  which  on  the  one  hand 
elucidates  the  importance  of  the  spaces  in  the  nutrition  of  the  epithelium,  on  the  other  hand  fur- 
nishes the  explanation  of  the  slight  size  of  the  spaces  and  bridges  in  the  simple  epithelia. 

?  See  also  the  Urinarv  Organs. 


8o 


HISTOLOGY. 


SECRETORY    ACTIVITY    OF    EPITHELIAL    TISSUE. 

Many  epithelial  cells  possess  the  faculty  of  secreting  and  discharg- 
ing substances  which  are  not  used  in  the  growth  and  repair  of  the 
tissues.  Such  cells  are  called  gland-cells.  The  secreted  substances  are 
either  stored  in  the  body  (secretions)  or,  being  of  no  further  use,  re- 
moved from  the  body  (excretions).  The  performance  of  the  processes 
of  elaboration  and  discharge  of  secretions  (or  excretions)  is  manifested 
by  certain  changes  in  the  form   and   contents   of  the   gland-cell,    which 


Granule. 


Granule.  . 


Protoplasm. 

Basal  filaments."  * 
Nucleus. 


Protoplasm. 


New  granule. 


Nucleus  with  large 
nucleolus. 


Fig.  24. — Two  Serous  Gland-cells  from  the  Submaxillary  Gland  of  a  Guinea-pig.  X  1260.  In 
cell  B  the  granules  have  passed  into  the  unstainable  state ;  new  stainable  granules  are  beginning  to 
develop  in  the  protoplasm.     Technic  No.  120. 

indicate  the  empty  and  the  loaded  f  condition,  states  of  rest  and  activity 
respectively.      In  many  cells,  for  example,  in  the  serous  gland-cells,  the 


*"-^ 


P- 


b 


P~i 


%MJ 


Fig.  25. — Secreting  Epithelial  Cells.  From  a  thin  section  of  the  mucous  membrane  of  the  stomach 
of  man.  X  560.  p.  Protoplasm,  s.  Secretion,  a.  Two  empty  cells;  the  cell  between  them  shows 
beginning  mucoid  metamorphosis,  e.  The  cell  on  the  right  is  discharging  its  contents ;  the  granular 
protoplasm  has  increased  and  the  nucleus  has  become  round  again.     Technic  No.  108. 

empty  state,  barring  certain  phenomena  of  the  nucleus  (p.  8i),  is  mani- 
fested by  a  smaller  volume  and  a  darker  appearance  of  the  cell ;  higher 


*  The  basal  filaments  occurring  in  the  serous  gland-cells  and  in  the  chief  cells  of  the  gas- 
tric glands  may  be  portions  of  the  filar  substance,  "  ergastoplasm,"  or  possibly  they  too  are  con- 
cerned in  the  production  of  the  secretion. 

f  The  terms  "  empty  "  and  "  loaded  "  relate  to  the  finished  secretion  and  its  impending 
discharge,  not  to  the  precursory  stages  ;  other  authors  employ  instead  the  expressions  "resting  " 
and  "  active.  " 


THE     TISSUES.  8 1 

objectives  and  special  methods  reveal  granules  *  that  stain  intensely 
(Fig.  24  A).  These  "granula"  grow,  lose  the  faculty  of  staining  (Fig. 
24  B),  and  become  transmuted  into  drops  of  secretion  ;  the  cell  there- 
with passes  into  the  loaded  state,  which  may  be  demonstrated  also  by 
simple  methods  and  is  indicated  by  an  increased  volume  and  a  clearer 
appearance.  The  drops  of  secretion,  occasionally  even  granules,  are 
discharged  into  the  lumen  of  the  gland.  In  other  gland-cells,  for  ex- 
ample, in  many  mucous  gland-cells,  the  elaboration  of  secretion  is  like- 
wise initially  associated  with  granules,  which,  however,  soon  become 
transformed  into  a  transparent  mass,  the  mucus  (Fig.  25,  s)  that  accu- 
mulates at  the  "collecting  center,  "  situated  on  the  side  of  the  cell  ad- 
jacent to  the  lumen  or  to  the  free  surface,  and  is  more  or  less  sharply 
defined  against  the  still  unaltered  protoplasm  (/;>,  /).f  As  the  process  of 
secretion  advances,  larger  and  larger  masses  of  the  protoplasm  are  con- 
verted into  secretion  and  the  nucleus  and  remnant  of  unaltered  proto- 
plasm are  crowded  to  the  base  of  the  cell ;  as  a  consequence  of  this  com- 
pression the  oval  nucleus  (a,  b)  gradually  becomes  round  {c)  or  even 
flat  (d).  The  volume  of  the  cell  when  filled  with  secretion  is  consider- 
ably increased.  Finally,  the  secretion  gradually  escapes  ;  simultane- 
ously the  protoplasm  is  regenerated  and  the  nucleus  moves  upward  to  its 
original  position,  and  restore  to  the  cell,  now  diminished  in  size,  the  ap- 
pearance of  the  empty  state. 

The  majority  of  gland-cells  do  not  degenerate  in  the  act  of  secre- 
tion, but  are  able  to  repeat  the  process  again  and  again.  The  sebaceous 
glands  furnish  an  exception,  for  their  secretion  is  formed  by  the  disinte- 
gration of  cells,  like  the  goblet-cells.^  In  the  latter,  in  one-layered 
epithelium,  the  processes  of  elaboration  and  expulsion  of  secretion  occur 
simultaneously  (Fig.  26)  ;  at  first  the  secretion  is  produced  more  rapidly 
than  it  is  discharged  and  it  accumulates  in  the  cell  (2),  but  finally  ex- 
pulsion exceeds  production,  the  cell  gradually  empties  itself  completely 
and  dies  (4).  In  stratified  or  many-rowed  epithelium  the  formation  of  se- 
cretion begins  in  the  young  goblet-cells  in  the  depths  of  the  glands  ;  the 
expulsion  does  not  occur  until  the  elements  have  matured  and  reached 
the  free  surface. 


*  These  are  not  the  microsomes  (p.  63)  stainable  by  certain  methods,  e.  g.  Altmann's 
methods. 

jThe  collecting  center  by  no  means  consists  only  of  secretion;  between  the  masses 
of  the  latter  there  is  a  delicate  net  or  framework  of  protoplasm,  that  also  encloses  the 
centrosome. 

j  The  testicle  and  the  ovary  afford  a  peculiar  instance,  the  gland-cells  of  which  after  dis- 
charge of  their  secretion  undergo  further  development. 
6 


82 


HISTOLOGY. 


The  gland-cells  lie  isolated  between  other  epithelial   cells  *   or  are 
united  in  groups  and  form  glandular'  tissue.     ♦ 

The  GLANDS.f 
The  glands,  glandulcB,  are  glandular  tissue  buried  beneath  the  sur- 
face   of  the  body,   which   either  has   the  form   of  cylinders,    tubidi,   or 
pouched  sacs,  alveoli. 


Secretion 
Protoplasm  with  nucleus 


Gland  lumen 


Fig.  26.— Crypt  of  Lieberkuhn  from  a  Section  of  the  Large  Intestine  of  Man.  X  165.  The 
secretion  formed  in  the  goblet-celis  is  deeply  stained.  In  zone  i  the  goblet-cells  show  the  beginning 
of  secretion  ;  that  expulsion  has  begun  is  evident  from  the  presence  of  drops  of  secretion  in  the  lumen 
of  the  crypt.  2.  Goblet-cells  with  much  secretion.  3.  Goblet-cells  containing  less  secretion.  4.  Dying 
goblet-cells,  some  of  which  still  contain  remnants  of  secretion.     Technic  No.  112. 

The  structure  of  glands,  in  particular  of  their  secreting  divisions,  is  easy 
to  recognize  only  when  they  present  simple  or  but  slightly  branched  tubuli  or 


*They  are  then  called  unicellular  glands;  they  are  very  common  among  invertebrates, 
also  occur  in  man  as  goblet-cells  (see  The  Digestive  Organs). 

f  The  glands  consist  almost  exclusively  of  epithelium  ;  supporting  tissue  and  blood- 
vessels, important  as  the  latter  are  in  a  physiologic  respect,  morphologically  are  relatively  sub- 
ordinate. This  furnishes  the  justification  for  describing  the  glands,  which  of  course  are  organs, 
as  the  conclusion  to  the  epithelial  tissues. 


THE     TISSUES. 


83 


alveoli.  The  majority  of  glands  are  profusely  branched,  twisted  and  coiled 
to  a  dense  ball,  that  can  scarcely  be  unravelled.  Sections  of  such  balls 
exhibit  clusters  of  vesicles  ("  acini  "),  that  may  be  equally  as  well  taken  for 
alveoli  as  for  cross-sections  of  tubuli.  This  explains  the  antagonistic  state- 
ments of  individual  authors.  Hitherto  the  only  dependable  method  for  the 
exhibition  of  the  gland  lumen  was  either  that  by  injection  or  by  impregnation 
of  the  secretion  after  Golgi.  If  the  lumen  appeared  in  the  shape  of  a  branched 
line  of  uniform  thickness,  it  was  inferred  that  the  form  was  tubular;  if  the 
lumen  exhibited  terminal  or  lateral  evaginations  the  structure  was  said  to  be 
alveolar.  Hitherto  I  also  made  my  classification  according  to  this  principle. 
It  was  of  course  incomplete,  since  it  did  not  include  any  consideration  of  the 
varying  thickness  of  the  wall.  Finally  the  plate  reconstruction  method  has 
led  to  recent  success  in  representing  the  entire  structure  (lumen  and  wall)  on 
an  enlarged  scale.  It  may  be  that  in  details  cor- 
rections must  still  be  made  ;  however  the  necessity 
for  a  new  classification  is  already  evident  and  is 
given  in  the  following. 

There  are  two  principal  forms  of  glands, 
the  tubular  and  the  alveolar*  glands.  Between 
these  two  there  is  a  transitional  form  origi- 
nating from  the  tubular  and  represented  by 
the  alveolo-tubular  glands.  All  three  forms 
occur  either  individually  independent  or  united 
in  groups  ;  they  are  accordingly  classified  as 
simple  and  compound  glands. 

A.    Tubular  glands. 

1.  Simple  t?{bular  glajtds,  which  have  the 
form  of  either  a  simple  or  a  branched  tube 
(Fig.  2y) ;  the  latter  form  may  be  named  a 
tubular  system. 

2.  Compound  Uibidar  glands,  wXvizh  con- 
sist of  a  variable  large  number  of  tubular  sys- 
tems (Fig.  27). 

Unbranched  simple  tubular  glands  are  the  following  :  some  of  the 
fundus  glands  of  the  stomach  ;  the  majority  of  the  coil  and  ceruminous 
glands,  and  the  intestinal  (Lieberkiihn's)  glands  (regarding  the  latter 
see  the  chapter  on  the  intestines). 

Branched  simple  tubular  glands  are  the  following  :  some  of  the 
fundus  glands,  a  few  of  the  coil  glands,  and  the  glands  of  the  uterus. 

Compound  tubular  glands  are  the  serous  glands  of  the  tongue,  the 
serous  divisions  of  the  small  glands  of  the  respiratory  apparatus  (and 
the  small  glands  of  the  oral  cavity?),  and  the  tear  glands.     Also  the 


Fig.  27. — Schemes  of  Tubular 
Gland  Forms. 


*  From  alveus,  a  pouched  sac. 


84 


HISTOLOGY. 


kidneys,  the  testicles,  and  the  liver.  The  ramifications  of  the  latter  two 
glands  anastomose  regularly  with  one  another  and  form  nets  ;  therefore 
the  testicles  and  the  liver  are  also  called  "  reticular  glands."  Isolated 
anastomoses  between  glands  have  been  observed  in  the  fundus  glands 
of  the  horse  and  in  the  serous  lingual  glands  and  the  bulbourethral 
glands  of  man. 

B.   Alveolo-tubular  glands. 

I .  Simple  alveolo-tubidar  glands  appear  to  occur  only  in  the  form  of 
branched  ducts  ;  they  form  an  alveolar-tubular  system  (Fig.  28). 


Alveolar 
tubular 
svstem. 


Alveolo- 
tubular 
compound 
gland. 


Excretory  duct. 


Alveolarsvstem. 


4  Excretor}' 


Fig.  28.— Schemes  of  Alveolo-tubular 
Gland  Forms. 


Fig.  2q.— Schemes  of  Alveol.'^r  Gland  Forms. 


2.  Compound  alveolo-tiibidar  glands,  which  consist  of  several  alve- 
olar-tubular systems  (Fig.  28). 

Branched  simple  alveolo-tubular  glands  are  the  pylorus  glands,  the 
urethral  glands,  and  the  small  mucous  glands  of  the  tongue,  the  gums, 
and  the  esophagus. 

Compound  alveolo-tubular  glands  are  the  larger  mucous  glands,  the 
sublingual  gland,  the  mucous  divisions  of  the  submaxillary  gland,  the 
glands  of  the  respiratory  apparatus  and  the  oral  cavity,  the  duodenal 
glands,  the  bulbourethral  glands  (vestibulares  majores  ?),  the  prostate, 
the  lungs,  and  the  mammary  glands. 


THE     TISSUES. 


^5 


Gland-lumen. 


Gland-cells. 


Membrana  pro- 
pria. 


,    Blood-vessels. 


C.   Alveolar  glands. 

1.  Simple  alveola)'-  glands  are  .simple  or  branched  pouched  sacs 
possessing  an  excretory  duct  (Fig.  29)  ;  the  branched  form  is  called  an 
alveolar  system. 

2.  Compound  alveolar  glands,  which  consist  of  several  alveolar  sys- 
tems (Fig.  29). 

Unbranched  simple  alveolar  glands  are  the  smallest  sebaceous 
glands. 

Branched  simple  alveolar  glands  are  the  larger  sebaceous  glands 
and  the  tarsal  (Meibomian)  glands. 

Compound  alveolar  glands  are  some  divisions  of  the  parotid  gland, 
the  serous  divisions  of  the  submaxillary  gland  (the   smallest  glands   of 
the  oral   cavity  ?),  and  the   pancreas.       In   all  the   compound  alveolar 
glands    slender    follicles,   partly   pro- 
vided  with    evaginations,    are    to    be 
found,   so  that  the  entire  glands  are 
to  be  annexed  to  the  alveolo-tubular 
glands,  with  the  reservation  that  they 
are    distinguished    from   the   alveolo- 
tubular  forms  by  the  predominance  of 
the  alveolar  type. 

In  the  majority  of  glands,  par- 
ticularly in  those  visible  to  the  naked 
eye,  a  sheath  is  formed  by  the  sur- 
rounding connective  tissue,  which 
sends  septa  into  the  gland  and  divides 
it  into  complexes  of  varying  size,  the 
gland  lobules.  The  septa  are  the  car- 
riers of  the  larger  blood-vessels  and  nerves.  The  glands  may  secrete 
throughout  their  entire  extent,  but  usually  only  that  part  lying  near  the 
blind  end,  the  gland  body,  is  specialized  for  this  purpose,  while  the  part 
forming  the  connection  with  the  surface  serves  for  the  conveyance  of  the 
secretion,  and  is  called  excretory  duct. 

Glands  xvithout  excretory  ducts  are  the  tliyroid  and  the  ovary.  The 
former  has  an  excretory  duct  in  the  embryonal  period,  which  disappears 
in  the  course  of  development ;  the  tubuli  also  suffer  change.  The  gland 
vesicles  ("follicles")  of  the  ovary  in  an  embryonal  period  also  w^ere  in 
connection  with  the  superficial  epithelium.  These  connections,  which 
might  be  called  excretory  ducts,  disappear,  and  the  expulsion  of  the 
products  formed  in  the  ovary  (the  ova)  takes  place  by  the  bursting  of  the 
vesicle.     The  ovary  is  a  dehiscent  gland. 


Fig.  30. — Section  of  a  Mucous  Gland  of 
THE  Tongue  of  a  Rabbit.  Blood-vessels 
injected.  The  nuclei  of  the  gland-cells 
were  indistinct.  X  iSo.  Technic  like  No. 
1256. 


86 


HISTOLOGY. 


All  gland  tubuli  and  alveoli  consist  of  a  usually  simple  layer  of 
gland-cells,  which  encircle  the  lumen  of  the  gland  and  are  in  turn  sur- 
rounded by  a  special  modification  of  the  connective  tissue,  the  viembrana 
propi^ia  or  basement-membrane  *  (see  p.  94).  On  the  outer  side  of  the 
basement-membrane  lie  the  blood-vessels  (Fig.  30).  Hence  the  gland- 
cells  are  inserted  between  the  blood-vessels  and  the  lumen  of  the 
gland,  and  on  the  peripheral  side  receive  from  the  blood-vessels  (or  from 
the  lymph  clefts  encircling  the  latter)  the  necessary  materials  for  the 
formation  of  secretion  and  on  the  other  (central  or  lumen)  side  discharge 

the   elaborated  product. 

Outlets  of  intracellular  and  intercellular  secretory  capillaries.  In  many  giands  the 

/  axial    (central)    lumen 

sends  off  delicate  lateral 
b  ra  n  ch  e  s ,  secretory  capil- 
laries, that  are  situated 
sometimes  between  the 
gland-cells,  "  intercellu- 
lar secretory  capillaries," 
sometimes  in  the  interior 
of  the  gland-cells,  "in- 
tracellular secretory  ca- 
pillaries."f  They  can 
be  made  visible  only  by 
special  methods  and  then 
appear  in  the  form  of 
sometimes  simple,  some- 
times branched,  or  even 
netlike,  '  anastomosing, 
tubules,  that  do  not  ex- 
tend  to    the    membrana 

propria  and  the  blood-vessels,  but  are  separated  from  these  by  at  least 

a  portion  of  a  gland-cell. 


Intracellular  secretory  ^-, 
capillary.  ' 


Intercellular  secretory  ,  -^ 
capillary.  \ 


Terminal  bars. 


Intercellular  secretory  capillary,  at  its  base  taking  up 
the  outlet  of  intracellular  secretory  capillaries. 

Fig.  31. — Schematic  Model  of  a  Human  Fundus  Gland. 


*  Occasionally  stellate  cells  occur  between  the  propria  and  tbe  gland-cells,  which  unite 
with  one  another  and  as  "basket  cells  "  embrace  the  gland  tubuli.  It  is  not  yet  decided 
whether  they  are  epithelial  or  connective  tissue  cells  or  smooth  muscle-fibers. 

fit  was  for  a  long  time  very  difficult  to  prove  whether  secretory  capillaries  were  situated 
between  or  within  the  cells.  Now  we  possess  points  of  corroboration  which  make  the  distinc- 
tion possible.  Intercellular  capillaries  in  cross-section  are  bordered  by  at  least  two  terminal 
bars  in  cross-section,  while  in  longitudinal  section  the  terminal  bars  are  seen  running  alongside 
the  walls  of  the  capillaries  (Fig.  31).  Further,  intercellular  capillaries  are  recognized  by  their 
sharp  outline,  which  is  due  to  a  thickening  of  the  exoplasm  (p.  63).  The  intracellular  capilla- 
ries lack  this  sharp  outline,  also  any  recognizable  relation  to  terminal  bars. 


THE     TISSUES. 


87 


Excretory 
duct. 


The  intercellular  secretory  capillaries  occur  in  the  serous  glands  of 
the  tongue,  in  the  parotid,  in  the  serous  divisions  of  the  submaxillary, 
the  sublingual  and  related  glands,  in  the  bulbourethral  glands,  in  the 
lacrimal  glands,  and  in  the  pyloric  glands.  Intercellular  and  intracel- 
lular secretory  capillaries  occur  side  by  side  in  the  coil-glands,  in  the 
liver,  and  in  the  gastric  glands.  It  is  probable  that  the  intracellular 
secretory  capillaries  are  merely  transient  formations. 

Secretory  capillaries  appear  to  be  wanting  in  the  pure  mucous 
glands,  in  the  mucous  divisions  of  the  mixed  glands,  in  the  intestinal, 
duodenal,  and  uterine  glands,  in  the  thyroid,  the  hypophysis,  and  the 
kidney. 

The  microscopic  appearance  of  the  gland-cells  changes  with  their 
periodic  functional  condition.  In  some  glands  all  the  cells  simultaneously 
exhibit  the  same  functional  appearance. 
In  other  glands  different  functional  states 
are  encountered  at  the  same  time,  even 
within  the  same  tubule  or  alveolus.  The 
latter  is  the  case  in  many  mucous  glands, 
in  which  the  loaded  cells  crowd  the  empty 
cells  more  or  less  completely  away  from 
the  lumen  of  the  gland  (see  also  the  chap- 
ter on  the  glands  of  the  oral  cavity).  The 
nuclei  of  many  gland-cells  also  exhibit 
varying  appearances  corresponding  to  the 
changing  functional  state  ;  often  in  empty 
cells  the  nucleus  exhibits  a  delicate  chro- 
matin network  and  a  conspicuous  nucle- 
olus, while  in  loaded  cells  the  nucleolus 
is  invisible  and  the  chromatin  cords  ap- 
pear in   the  form  of  coarse  fragments.* 

The  finer  ramifications  of  the  excretory  ducts  of  some  glands, 
which  are  particularly  conspicuous  because  of  the  form  and  structure  of 
their  epithelial  cells,  must  be  regarded  as  belonging  to  the  gland  body. 
These  ramifications  are  not  merely  excretory  ducts,  but  on  them  also 
devolves  the  function  of  excreting  certain  materials  (salts)  ;  accordingly 
they  belong  to  the  secreting  divisions  of  the  glands.  The  difference  in 
the  structure   of  these   branches   renders   their   division  into  two  parts 


1 

Secretory 
tube. 

^£. 

iQ      Intercalated 

\    m" 

^>       tubes. 

-^<p 

^w^ 

f>^— — 

l^i=.    End  pieces. 

^ 


Fig.  32.  Schematic  drawing  of  the  dif- 
ferent divisions  of  a  gland.  (Sub- 
maxillary of  man.) 


*  There  is  no  doubt  that  portions  of  the  nucleus,  in  the  form  of  stainable  granules,  pass 
into  the  protoplasm,  but  whether  these  portions  may  be  regarded  as  true  secretion  granules  is 
questionable;  the  more  so  since  such  phenomena  may  be  observed  in  other  cells,  for  example, 
in  the  cells  of  the  spinal  ganglia. 


88  HISTOLOGY. 

desirable  :  the  first  portion,  proceeding  from  the  terminal  pieces,'^  is  nar- 
row and  lined  sometimes  with  flat,  sometimes  with  cubical  cells  ;  it  is 
called  the  intercalated  tiibiile.  The  adjoining  portion  is  wider  and  clothed 
with  tall  cylinder  cells,  the  bases  of  which  show  distinct  longitudinal 
striation,  formed  by  rows  of  granules  ;  it  is  called  the  secretory  {salivary 
or  mucous^  tube.  The  relative  length  of  the  intercalated  and  secretory 
tubes  varies  greatly  in  individual  glands. 

The  excretory  ducts  consist  of  a  simple  or  stratified  cylinder  epithe- 
lium and  a  sheath  of  connective  tissue  mingled  with  elastic  fibers. 

Accordingly  in  the  most  complicated  cases  the  gland  consists  of 
the  following  divisions  :  (i)  The  excretory  duct,  which  dividing  passes 
into  (2),  the  secretory  tubes,  which  continue  in  (3),  the  intercalated  por- 
tions, which  lead  into  (4),  the  terminal  pieces,  the  axial  lumen  of  which 
receives  (5),  the  secretory  capillaries. 

TECHNIC. 

No.  2. — Living  ciliated  cells  are  obtained  as  follows  :  Kill  a  frog 
(p.  28),  place  it  on  its-  back,  and  with  scissors  cut  off  the  lower  jaw,  so 
that  the  roof  of  the  cavity  of  the  mouth  is  exposed.  From  the  mucosa 
of  the  roof  cut  out  a  small  strip  about  5  mm.  long,  place  it  on  the  slide 
in  a  drop  of  salt  solution,  and  apply  a  cover-glass.  With  low  magnifica- 
tion the  beginner  will  scarcely  perceive  anything,  unless  currents  in 
which  large  blood  corpuscles  are  suspended  lead  him  to  the  right  place  ; 
therefore  examine  with  the  high  power  and  search  the  edges  of  the 
preparation.  At  first  the  movement  of  the  cilia  is  so  lively  that  the  ob- 
server cannot  see  individual  cilia ;  the  entire  ciliated  border  waves  ; 
the  picture  has  been  aptly  compared  to  that  of  a  corn-field  swayed 
by  the  wind.  After  a  few  moments  the  rapidity  of  the  movement  dimin- 
ishes and  the  cilia  can  be  plainly  seen.  If  the  movement  ceases,  it  can 
be  restored  by  the  application  of  a  drop  of  concentrated  potash  solution 
(p.  23)  ;  the  effect  is  transient,  so  that  the  eye  of  the  observer  must  not 
be  removed  from  the  ocular  while  the  fluid  passes  under  the  cover- 
glass.      The  addition  of  water  soon  suspends  the  movement. 

No.  3. — Tcrniinal  bars. — Fix  small  pieces  of  intestine,  from  0.5  to 
I  cm.  long,  in  Flemming's  rnixture  (p.  34),  or  in  sublimate -salt  solution 
(p.  35),  and  harden  in  alcohols  of  gradually  increased  strength  (p.  35); 
embed  in  paraffin,  cut  thin  sections  (about  10  /i)  on  the  microtome,  and 
fasten  them  to  the  slide  (see  Microtome  Technic).  Stain  after  Heiden- 
hain's  iron-hematoxylin  method  (p.  44),  and  mount  in  xylol-balsam. 
The  bars  can  be  distinguished  as  black  streaks  or  dots,  even  with  good 
dry  systems  (Fig.  21).  With  immersion  systems  the  centrosomes  can 
be  seen  in  such  preparations,  but  only  the  practiced  microscopist  can 
succeed  in  finding  them. 

*  This  is  the  designation  of  the  blind  ends  of  the  gland  ducts,  which  take  up  the  secre- 
tory capillaries. 


THE     TISSUES. 


89 


II.    THE   SUPPORTING   TISSUES. 

In  the  epithelial  tissues  the  cells  constitute  the  principal  mass,  but 
in  the  supporting  tissues  they  are  secondary,  while  the  intercellular  sub- 
stance (ground  substance,  matrix)  is  conspicuously  developed  and  variously 
differentiated.  The  preponderance  of  the  intercellular  substance,  which 
also  functionally  plays  the  more  important  part,  is  characteristic  of  the 
group  of  supporting  tissues.  According  to  the  nature  of  the  intercellu- 
lar substance  they  are  divided  into  :  (i)  connective  tissue  ;  (2)  cartilage  ; 
(3)  bone. 

I.   Connective   Tissue. 

The  matrix  or  intercellular  substance  of  connective  tissue  is  more 
or  less  soft ;  the  cells  are  i^w  in  number.  Several  varieties  are  distin- 
guished :  {a)  mucous  connective  tissue, 
ili)  fibrillar  connective  tissue,  and  {c)  re- 
ticular connective  tissue. 

{ci)  Mucous  connective  tissue  consists 
of  round  or  stellate  branched  cells  and 
a  large  quantity  of  undifferentiated,  mu- 
ciferous  intercellular  substance  contain- 
ing delicate  connective-tissue  bundles 
(see  below).  In  the  higher  animals  it  is 
found  only  in  the  umbilical  cord  of  very 
young  embryos,  but  it  is  widely  distrib- 
uted in  many  lower  animals.* 

{p)  Fibrillar  connective  tissue  con- 
sists of  abundant  intercellular  substance  and  of  cells. 

The  intercellular  substance  consists  of  connective-tissue  fibrillse 
(connective-tissue  fibers), f  exquisitely  fine  filaments  (0.6  /^),  which  are 
united  by  a  small  quantity  of  homogeneous  cement  substance  into  bun- 
dles of  varying  thickness,  the  connective-tissue  bundles.  These  bundles 
are  soft,  flexible,  slightly  extensible,  are  characterized  by  their  pale 
contours,  their  longitudinal  striation,  their  wavy  course, |  and  by  their 
chemical  properties.  On  treatment  with  picric  acid  they  separate 
into  their  fibrils,  swell   on  the  addition  of  dilute    acids,  r.  ^.,  acetic  acid, 


Fig.  33.— From  a  Cross-section  of  the 
Umbilical  Cord  of  a  Human  Embryo 
about  Four  Months  Old.  X  240.  i. 
Cells.  2.  Intercellular  substance.  3. 
Connective-tissue  bundles  mostly  in 
oblique  section,  at  4  in  true  cross-sec- 
tion.    Technic  No.  4. 


*  Regarding  the  vitreous  body,  which  some  authors  hold  consists  of  mucous  tissue,  see  the 
chapter  on  the  vitreous  body. 

t  Here  fihyilhz  and  fibers  are  synonymous,  while  in  the  striated  elements  of  muscle  tissue 
a  number  of  fibrillse  form  a  fiber. 

%  Hence  the  name  -wavy  or  curly  connective  tissue. 


go  HISTOLOGY. 

and  become  completely  transparent,  are  destroyed  by  alkaline  fluids, 
and  on  boiling  yield  ghitin.  The  substance  of  the  glutin-yielding  con- 
nective tissue  is  called  collagen. 

According  to  one  view  the  first  connective-tissue  fibrils  originate  in 
the  intC7-ior  of  the  cell  ;  on  another  theory  they  arise  external  to  the  cell 
and  in  the  latter  case  are  a  metamorphosis  of  the  ground  substance.* 

The  ground  substance  of  fibrillar  connective  tissue  invariably  con- 
tains elastic  fibers,  but  in  fluctuating  quantity  (Fig.  35).  They  are 
characterized  by  their  sharp,  dark  outlines,  their  strong  refractive  power, 
and — in  contrast  with  the  connective-tissue  bundles — their  extraordinary 


Fat  drops. 


Fat-cells. 


Connective-tissue  Nucleus  of  a  connective- 

bundles,  tissue  cell. 


>t\\  / 


Fig.  34. — CoNNKCTivE-TissuE  Bundles  of  Different  Thicknesses  from  the  Intermuscular 
Connective  Tissue  of  Man.    X  320.    Technic  No.  5. 

resistance  to  acids  and  alkalies.  The  substance  of  the  elastic  fibers  is 
named  elastin.\  The  elastic  fibers  vary  from  immeasurably  fine  to  1 1  fi, 
and  usually  occur  in  the  form  of  finer  or  coarser  networks,  the  meshes 
of  which  are  sometimes  narrow,  sometimes  large. 


*  Flemming  holds  that  a  fibril-containing  stratum  is  formed  in  the  peripheral  portion  of 
the  cell,  which  separating  becomes  intercellular  substance  and  as  such  can  produce  new  fibrillse. 
Perhaps  the  different  opinions  are  harmonized  in  this  statement. 

f  There  are  cases,  chiefly  pathologic, — for  example  in  the  withered  skin  of  the  face  of 
aged  persons — in  which  the  elastic  fibers  stain  weakly  with  specific  acid  dyes  (No.  13,  p.  43) 
and  on  the  other  hand  react  strongly  with  basic  dyes ;  the  substance  of  such  fibers  is  called 
elacin.  Contrawise,  degenerating  fibers  of  glutinous  connective-tissue  stain  strongly  with  the 
specified  acid  dyes;  this  modified  substance  of  connective  tissue  has  been  named  collastin. 


THE     TISSUES. 


91 


Narrow-meshed  networks  composed  of  thick  elastic  fibers  form  the 
transition  to  elastic  membranes  (Fig.  36),  which  are  either  homogeneous 
or  finely  striated  and  are  perforated  with  holes  of  different  sizes  (hence 
the  name  fenestrated  membranes),  and  doubtless  are  produced  by  the 
fusion  of  broad  elastic  fibers. 


a, 


^a^^ 


'Q 


Or'.^^UP/ 


'd^ 


Fig.  35. — Elastic  Fibers.  X  560.  A.  Fine  elastic  fibers:  /,  from  intermuscular  connective  tissue  of 
man  ;  b,  connective-tissue  bundles  swelled  by  treatment  with  acetic  acid.  Technic  No.  12.  B.  Very 
thick  elastic  fibers  :  f,  from  the  ligamentum  nuch«  of  an  ox  ;  b,  connective-tissue  bundles.  Technic 
No.  13.  C.  From  a  cross-section  of  the  ligamentum  nucha;  of  an  ox  ;  f,  elastic  fibers  ;  b,  connective- 
tissue  bundles.     Technic  No.  14. 


When  the  quantity  of  elastic  fibers  predominates  over  the  number 
of  connective-tissue  bundles,  the  tissue  is  spoken  of  as  elastic  tissue. 

Hitherto  the  elastic  fibers  were 
regarded  as  transformations  of  the 
ground  substance  (perhaps  of  the  ex- 
isting connective-tissue  bundles)  ;  ac- 
cording to  recent  investigations  they 
are  held  to  originate  in  the  cells,  in 
the  form  of  the  minutest  depositions, 
that  fuse  into  delicate  nets  ;  then  the 
cells,  it  is  supposed,  degenerate, 
whereby  the  fibers  are  liberated  (?). 
In  the  beginning  of  their  develop- 
ment the  elastic  fibers  are  thin,  but 
progressively   with    their    growth   increase   in  thickness   by    apposition. 

The  cells  (Fig.  37  A)  are  irregularly  polygonal,  plump,  and  process- 
less  ;  or  stellate  with  processes,  strongly  flattened  and  variously  bent  or 
indented.  The  compression  and  notching  are  explained  by  the  adapta- 
tion  of  the  cells  to  the  narrow  spaces  occurring  between  the  connective- 


m      -  n 

Fig.  36. — Network  («)  of  thick  elastic  fibers, 
on  the  left  passing  into  a  fenestrated 
membrane,  m.  From  the  endocardium 
of  man.     X  560.     Technic  No.  15. 


92  HISTOLOGY. 

tissue  bundles.  Not  infrequently  the  flattened  cells  form  complete 
sheaths  about  the  connective-tissue  bundles.*  If  such  a  bundle  be 
treated  with  acetic  acid  it  swells  and  bursts  the  ensheathing  cells,   of 

which    annular    or    other- 
\  .;  \         /^  ,,W"  shaped    fragments     remain 


u/j         x-i                    /  V               ^^  and    constrict   the   swelled 

Il|p7\                             /       -, "  bundle.       Formerly    these 

'  f\'^''             '^              /      Vl  /  il  remnants  of  cells  were  con- 

^"■1  sidered     fibers     and    were 

"}  called  "encircling   fibers" 

^,  (Fig-  37  B). 

"  .    \  The  protoplasmic  body 

of  the  connective-tissue  cell 

encloses     a     nucleus     and 

o  f  t  e  n     contains     pigment 

Fig.  37. — A.  Connective-tissue  cells  from  intermuscular  con-  ,             •       ^.i        1    ^i. 

nective  tissue.  X  560.  i.  Flat  cell  lying  partly  on  a  con-  granulCS  ;  m  the  latter  CaSC 
nective-tissue  bundle;  2,  notched  cell ;  3,  nucleus  of  a  cell,  .  //  1 
the  protoplasm  is  invisible;  6,  connective-tissue  bundles.  tnCy  DeCOtne.plP'7n£'flt  C£//S,J 
Technic  No.  6.  5.  Connective-tissue  bundles  with  encirc- 
ling fibers;  -4,  nucleus.  Technic  No.  9.  C.  Plasma-cells  that  in  man  are  found  Only 
from  the  eyelid  of  a  child.      Technic  No.  191. 

in     certain     areas     of    the 


f] 


c     ,.-^^.-. ... 

\ 

\ 

..,r'.^© 

" 

'^\ 

m..m  ^ 

li^ 

skin  and  in  the  eye,  but  in  the  lower  animals  are  very  widely  distributed. 
Connective-tissue  cells  may  contain  fat  globules,  that,  when  they  are 
very  large,  coalesce  and  give  a  spherical  form  to  the  cell,  which  is  then 
designated  2.  fat-cell  (Fig.  38).  In  such  cells 
the  protoplasm  occupies  only  a  narrow  per- 
ipheral zone,  in  which  lies  the  extremely  flat- 
tened nucleus,  that  in  well-developed,  but  not 
in  atrophic,  fat-cells  invariably  contains  one 
or  more  sharply  circumscribed  fat  droplets 
(Fig.  39).      The  protoplasmic  zone  often  is  so      fig.  ss.— fat-cells  from  the 

,...,,  .  .  -    -  Axilla  OF  Man.   X  240.    r.The 

thm  as  to  be  mvisible.      Aggregations  ot  tat-  equator  of  the  ceii  in  focus;  2, 

objective  somewhat   elevated  ; 
cells  lead    to    the    construction   of   a    formation  3,4,  forms  changed  by  pressure; 

p.  traces  of  protoplasm  in  the 

interwoven     with      numerous     blood-vessels,  ^i^inity  of  the  flat  nucleus,  k. 

Technic  No.  lo. 

lymph-vessels,     and     nerves,     called     adipose 

tissue,  which    plays    a   very   important   physiologic   role   in    connection 

with  metabolism. 

*  The  form  of  the  connective-tissue  cells  is  not  in  any  respect  characteristic  ;  especially 
when  they  lie  together  in  groups  their  resemblance  to  epithelial  cells  often  is  complete.  Regard- 
ing the  true  nature  of  such  elements,  designated  by  the  perilous  name  of  "  epithelioid  "  cells, 
the  embryonal  history  alone,  not  the  form,  can  give  the  solution. 

f  Not  every  pigment  cell  is  a  connective-tissue  cell;  there  are  also  pigmented  epithelial 
cells,  e.  g.,  in  the  eye. 


THE     TISSUES. 


93 


In  high  degrees  of  emaciation  fat-cells  are  found  in  which  all  thefat 
except  a  few  tiny  drops  has  disappeared  and  in  place  of  it  there  is  a  pale 
protoplasm  mixed  with  a  mucoid  fluid  ;  the  cell  is  no  longer  spherical, 


Surface-view  of  fat-cells,  in  the  nuclei  of  \fhich  fat  droplets  are  visible. 


Connective-tissue      Blood-vessel  with 
cells.  blood-cells. 


Blood  capillary. 


Fibrillar  connective  tissue. 


A  fat-cell,  with  its  nucleus 
in  profile. 

Fig.  39. — Adipose  Tissue  from  the'Human  Scalp.     X  240  (about).    Technic  No.  11. 


but  has  become  flattened.  Such  cells  are  named  serous  fat-cells  {¥\g.  40). 
In  many  fat-cells  spherical  masses  of  needle-shaped  crystals,  the  so- 
called  margariii  oystals,  appear  after  death. 

Finally,  cells  are  found  in  connective 
tissue  that  are  not  connective-tissue  elements, 
but  leucocytes  (see  p.  137)  that  have  passed 
out  of  the  blood-vessels.  They  are  described 
as  tvandering  cells,  to  distinguish  them  from 
the  connective-tissue  cells,  which  are  desig- 
nated fixed  cells ;  a  clas-sification  that  cannot 
be  rigidly  carried  out,  since  in  some  con- 
ditions (mainly  pathologic)  the  fixed  connec- 
tive-tissue cells  can  migrate  ;*  therefore  it  is 
better  to  term  the  latter  "  histogenetic,"  the 
wandering  leucocytes  "  hematogenetic  "  wan- 
dering cells. 

The   plasma-cells  and    mast-cells   occurring    in    fibrillar   connective 
tissue  in  widely  varying  quantity  must  be  regarded  as  peculiar  forms  of 


^'^^ 


Fig.  40. — Serous  Fat-cells  from 
THE  Axilla  of  an  Extremely 
Emaciated  Indi\'idual.  X  240. 
k.  Nucleus;  y,  oil-droplets,  c, 
Blood  capillaries;  lii,  connective- 
tissue  bundles.    Technic  No.  10. 


*  Under  like  conditions  epithelial  and  gland-cells  can  wander;  it  is  self-evident  that  such 
wandering  cells  cannot  be  included  in  the  same  categorv  with  the  leucocytes. 


94 


HISTOLOGY. 


leucocytes.  The  former  are  found  principally  in  the  vicinity  of  small 
blood-vessels  and  are  spherical,  coarsely  granular,  rich  in  protoplasm, 
and  relatively  of  large  size  (Fig.  37)  ;  the  latter  contain  granules  that 
are  easily  stained  by  anilin  dyes  (e.  g.  dahlia),  but  do  not  stand,  as  their 
name  may  suggest,  in  any  demonstrable  relation  to  nutrition.  Here 
also  belong  the  clasmatocytes,  branched  cells  the  processes  of  which 
sever  from  the  body  (whence  the  name),  dissolve,  and,  it  is  said,  con- 
tribute to  nutrition. 

distribution  of   the  different   kinds  of  cells  are 
/        subject  to  considerable  fluctuation. 


The  number  and 


The  different  elements  of  fibril- 
lar connective  tissue  are  united 
either  without  exact  arrangement, 
as  "  formless  "  (areolar)  connec- 
tive tissue  or  are  regularly  dis- 
posed in  definite  formations,  as 
"formed"  connective  tissue.  Form- 
less connective  tissue  is  distin- 
gjjished  by  its  loosely  united 
fiber-bundles  interlacing  in  every 
direction ;  it  occurs  between  neigh- 
boring organs  and  serves  to  con- 
nect them  and  fill  in  the  inter- 
spaces. For  this  reason  it  is  called 
"  interstitial  "  tissue.  The  cells  of 
interstitial  tissue  not  infrequently 
contain  fat.  ^\\q.  formed  connective 
tissue  is  characterized  by  the  inti- 
mate union  and  regular  arrange- 
ment of  its  bundles  and  comprises 
the  corium,  the  mucous  membranes,  the  serous  membranes,  the  peri- 
osteum, the  perichondrium,  the  tendons,  the  fasciae,  the  ligaments  ;  the 
compact  sheaths  of  the  central  nervous  system,  of  the  blood-vessels,  of 
the  eye,  and  of  many  glands. 

Where  fibrillar  connective  tissue  is  in  immediate  contact  with  epi- 
thelium it  not  infrequently  happens  that  a  structureless  membrane  is 
formed,  described  as  basement  membrane  or  mcmbrana  propria,  also 
hyaloid  membrane.  It  is  essentially  a  modification  of  the  connective 
tissue  ;  possibly  here  and  there  on  the  epithelial  side,  a  product  of  the 
epithelium. 

{c)  Reticular  connective  tissue. — The  views  in  regard  to  the  struc- 


'i///^ 


Fig.  41. — "  Formed"  Connective  Tissue.  A 
Piece  of  the  Greater  Omentum  of  Man. 
X  60.    Technic  No.  i6. 


THE     TISSUES. 


95 


ture  of  reticular  connective  tissue  are  divided.  According  to  an  opinion 
formerly  widely  entertained  it  consists  of  a  delicate  network  of  anasto- 
mosing stellate  cells.  To  this  may  be  traced  the  name  "  cytogenous," 
that  is,  formed  of  cells.*  There  is  no  doubt  that  such  networks  exist 
in  lower  vertebrate  animals  and  irt  embryonic  stages  of  higher  vertebrate 
animals,  but  occur  only  seldom  in  adults.  In  the  higher  vertebrates  the 
relations  are  changed  ;  here  the  network  consists  of  slender  bundles  of 
fibrillar  connective  tissue,  upon  which  lie  flattened,  nucleated  cells  (Fig. 
42).  By  means  of  complicated  methods  the  outlines  of  the  cells  on  the 
fibers  can  be  demonstrated.  In  fibrillar  connective  tissue  the  cells  almost 
without  exception  lie  upon  the  bun- 
dles. Finally,  the  fact  that  even  in 
the  adult  fibrillar  connective  tissue 
may  change  into  reticular  tissue  can 
be  comprehended  only  on  the  as- 
sumption that  the  latter  is  a  network 
of  delicate'  fiber  bundles.  Therefore 
reticular  connective  tissue  really  is 
only  a  variety  of  the  fibrillar  tissue, 
differing  somewhat  from  the  latter 
chemically,  in  its  greater  resistance 
to  reagents.  The  meshes  of  reticu- 
lar connective  tissue  are  invariably 
filled  with  densely  crowded  leucocytes.  It  occurs  principally  in  lymph 
glands  (better  lymph  nodes)  ;  for  this  reason  it  is  called  adenoid  tissue, 
that  is,  tissue  resembling  glands. 


Leuco 
cvles 


Fig.  42.— Reticular  Connective  Tissue.  From 
a  shaken  section  of  a  human  lymph-gland. 
X  560.     Technic  No.  55. 


2.    Cartilage. 

Cartilage  is  firm,  elastic,  easily  cut,  and  milk-white  or  yellowish  in 
color.  The  cells  present  little  that  is  characteristic  in  form  ;  usually  they 
are  spherical  or  flattened  on  one  side.  They  lie  in  cavities  in  the  ground 
substance, t  which  they  completely  fill  (Fig.  43).  Not  seldom  the  matrix 
immediately  surrounding  the  cavities  is  specialized  and  forms  a  highly 
refractive,  occasionally  concentrically  striated  shell,  the  cartilage  capsule. 
The  matrix  originates  in  excretions  of  the   cells,  through   the   capsules, 


*  Accordingly  mucous  tissue  also  might  be  termed  cytogenous  tissue. 

"f  Whether,  as  in  osseous  tissue,  the  cavities  are  united  with  each  other  by  a  system  of 
minute  canals  buried  in  the  matrix  is  still  extremely  doubtful.  Many  such  observations  have 
been  acknowledged  as  erroneous.  The  supposed  canaliculi  were  due  to  shrinkage  of  the 
matrix  and  can  be  produced  by  treating  cartilage  with  absolute  alcohol  or  with  ether. 


96 


HISTOLOGY. 


which  fuse  into  a  homogeneous  mass.*  The  parts  of  the  capsule 
lying  nearest  to  the  cells  are  the  youngest ;  they  do  not  always  persist, 
but  during  the  process  of  cell-division  are  resorbed.  Consequently  the 
ground  substance  is  subject  to  many  changes.  It  may  be  free  from 
fibrous  admixture  or  it  may  be  penetrated  by  elastic  fibers  or  by  con- 
nective-tissue bundles.  Accordingly  three  varieties  are  distinguished  :  («) 
hyaline  cartilage,  (/;)  elastic  cartilage,  (c)  fibrous  cartilage. 

{a)  Hyaline  cartilage  is  of  a  faint  bluish,  pearly  color.      It  occurs  in 
the  cartilages  of  the   respiratory  organs  and  of  the  nose,  as  the  costal 


Protoplasm  'j 

•tp  /-of  a  cartilage  cell 


Nucleus    Piotoplasm    Lacuna.    Capsule. 

Fig.  44. — Section  of  a  Human  Costal  Cartilage,  ex- 
amined Several  Days  after  Death.  The  proto- 
plasm has  withdrawn  from  the  wall  of  the  lacuna. 
At  X  two  cells  lie  in  one  capsule.  X  300.  Technic 
No.  iS. 
The  shaded  cells  do  not  lie  in  the   ocal  plane  and  therefore  shimmer  indistinctly  through. 


Fig.  43. — Surface  Picture  of  a  Piece 
OF  the  Fresh  Ensiform  Process  of 
a  Frog.     X  300.     Technic  No.  17. 


and  the  articular  cartilages,  also  in  the  synchondroses,  and  in  the  embryo 
in  many  situations  where  later  it  is  replaced  by  bone.  It  is  characterized 
by  the  homogeneity  of  its  matrix,  which  in  the  ordinary  methods  ot 
investigation  appears  amorphous  throughout,  but  after  certain  manipula- 
tions, e.  g.,  artificial  digestion,  falls  apart  into  bundles  of  fibers.  Fur- 
ther evidence  in  corroboration  of  the  fibrillar  structure  of  the  ground 
substance  is  afforded  by  its  behavior  in  polarized  light.  It  is  very  firm, 
very  elastic,  and  on  boiling  yields  cJiondrin. 


*  According  to  recent  investigations  the  cartilage  capsules  are  said  to  originate  from  the 
exoplasm  of  the  cartilage  cells  ;  in  this  case  the  matrix  is  not  a  secretion,  but  a  transformation 
product  of  the  cartilage  cells. 


THE     TISSUES. 


97 


In  certain  cases  the  matrix  may  undergo  peculiar  modifications.  In 
the  laryngeal  and  costal  cartilages  it  is  transformed  patchwise  into  rigid 
fibers,  that  impart  an  asbestos-like  luster,  perceptible  on  macroscopic 
inspection.  In  advanced  age  *  deposition  of  calcareous  salts  may  take 
place  in  the  hyaline  matrix,  in  the  beginning  appearing  in  the  form  of 
minute  granules,  subsequently  as  complete  husks  surrounding  and 
enclosing  the  cells. 

The  cells  of  hyaline  cartilage  frequently  occur  in  groups  or  nests, 
an  arrangement  explained  by  the  conditions  and  processes  of  growth. 
Two  cells  may  be  seen  within  the  same  capsule  (Fig.  44,  X)  ;  they  are  the 
descendants  of  one  cartilage  cell  which  has  undergone  division  by  the 
indirect  mode  ;  in  other  cases  a  thin  partition  of  hyaline  substance  may 
be  seen  between  two  such  cells.  In  still  other  cases  the  septum  does 
not  develop  immediately,  and  the  process  of  cell-division  may  be  repeated 


0 


i,j._it:-:jfi 


5*7 /■■'*?■  »*'i  i-sfe-'vi.' 


Si'^^' 


tM:p 


Fig.  45.— Elastic  Cartilage.  X  240.  i.  Portion  of  a  section  of  the  vocal  process  of  an  arytenoid  car- 
tilage of  a  woman  thirty  years  old  ;  the  elastic  substance  is  in  the  form  of  granules.  2  and  3.  Portions 
of  sections  of  the  epiglottis  of  a  woman  sixty  years  old  ;  a  fine  network  of  elastic  fibers  in  2,  a  denser 
network  in  3.    z.  Cartilage-cell,  nucleus  invisible  ;  k,  capsule.    Technic  No.  19. 

until  groups  of  four,  eight,  and  even  more  cells  may  be  enclosed  within 
one  capsule  (Fig.  44).  Such  phenomena  were  supposed  to  establish  a 
special  theory  of  cell-division,  the  so-called  endogenous  cell-formation 
{cf.  p.  72).  Not  infrequently  the  cartilage  cells  in  adults  contain  oil- 
globules. 

{It)  Elastic  cartilage  has  a  faint  yellowish  color.  It  occurs  only  in 
the  external  ear,  the  epiglottis,  the  cuneiform  and  corniculate  cartilages, 
and  the  apex  and  vocal  process  of  the  arytenoid  cartilages.  It  presents 
the  same  structural  features  as  hyaline  cartilage,  but  is  distinguished  by 
the  networks  of  sometimes  finer,  sometimes  coarser  elastic  fibers  that 
penetrate  the  matrix.  The  elastic  fibers  do  not  arise  directly  from  the 
cartilage-cells,  but  by  a  transformation  of  the  matrix,  and  appear  in  the 
vicinity  of  the  former  as  minute  granules  (Fig.  45,  i),  that  later  are  dis- 


In  the  cartilages  of  the  larynx  this  may  occur  as  early  as  the  twentieth  year. 


98  HISTOLOGY. 

posed  in  linear  rows  and  fuse  into  fibers.  According  to  an  opposite 
view,  this  phenomenon  is  regarded  as  an  indication  of  post-mortem  dis- 
integration of  the  elastic  fibers. 

(c)  Fibroiis  cartilage  (connective -tissue  cartilage)  is  found  in  the  in- 
tervertebral disks,  the  pubic  symphysis,  the  head  of  the  ulna,  the  artic- 
ular ends  of  the  maxilla,  the  sternum,   the  clavicle,  and  the  ribs.      The 
matrix  contains  an  abundance  of  fibrillar  connective  tissue,  the  loose  bun- 
dles of  which  extend  in  every  direc- 
'     \  tion  (Fig.  46,  g).       The  cartilage-cells 

A  are  iftv^  in  number,  have  thick  capsules 


'  -i 


I    11'' 


k 


V  (5),  and  lie  united  in  small  groups  or 

rows  at  wide  intervals. 

3.    Osseous  Tissue. 

i  <S  '  •                     The  matrix  of  bone  (osseous  tis- 

"^^  sue)  is  distinguished  by  its  hardness, 

I  'I' I  \\'  '                 solidity,  and  elasticity,  properties  due 

{                        '  '  to  an  intimate  blending  of  organic  and 

Fig.  46.— From  A  Horizontal  Section  of  inorganic  SubstanceS.*        It  is  COmpOSCd 
THE  Intervertebral    Disk  of  Man.  °  ^ 

^.  Fibrillar  connective  tissue;    ^,  carti-  of   calcium    SaltS,    chicfly    basic    CalciUm 
lage-cell   (nucleus  invisible)  ;   k,  capsule  '  •' 

X  24o?"Te1:hnk  No^'2o.'''°"'   g-"^""'^^-     phosphatc,    and   of  collagcnous    fibrils 

that  are  united  by  a  small  amount  of 
cement  substance  in  fine  or  coarse  bundles  ;  accordingly,  a  fine-fiber ed, 
or  lamellar,  and  coarse fibered,  or  plexiform,  bone-matrix  are  distin- 
guished.f  It  appears  homogeneous  or  faintly  striated  and  contains 
numerous  spindle-shaped  spaces,  15  to  27  //  in  length,  the  bone 
lac2in(S  (formerly  called  "bone  corpuscles"),  which  communicate  with 
one  another  through  numerous  branched,  minute  canals,  the  bone 
£analicidi.  In  this  way  a  system  of  canaliculi  that  penetrates  the  entire 
matrix  is  established.     Within  the  lacunae,  sometimes  improperly  called 

*This  union  is  of  such  a  nature  that  either  part  may  be  removed  without  destroying  the 
structure  of  the  tissue.  On  treatment  with  acids  (see  Decalcifying,  p.  36)  the  inorganic  sub- 
stances are  withdrawn  ;  the  bone  is  decalcified,  is  rendered  flexible,  and  is  easily  cut,  like  car- 
tilage;  therefore  it  is  called  "bone  cartilage."  The  organic  substances  can  be  removed  by 
cautious  heating  ;  the  bone  then  is  said  to  be  calcined.  Similarly,  fossil  bones  are  deprived  of 
the  organic  substances  through  the  prolonged  action  of  moisture. 

•f"  The  skeleton  of  the  adult  is  principally  formed  of  the  fine-fibered  matrix,  which  is 
characterized  by  distinct  lamellae  (see  The  Organs  of  the  Skeletal  System)  ;  it  contains  elastic 
fibers.  The  coarse-fibered  matrix  occurs  in  the  fetus  in  perichondral  and  secondary  bone  (see 
Development  of  Bone),  and  is  found  in  the  adult  in  sutures  and  at  the  point  of  insertion  of 
tendons  ;  it  always  contains,  partly  calcified,  partly  uucalcified,  connective-tissue  bundles,  the 
so-called  Sharpey's  fibers,  which  also  are  found  in  the  circumferential  and  interstitial  lamellae 
of  fine-fibered  bone. 


THE     TISSUES. 


99 


"bone-cells,"   lie   the   nucleated   l?o/it'-ce//s  (Fig.  4S),  which  have  a  flat- 
oval  shape  and  send  thin  processes  into  the  bone  canaliculi.     It  is  doubt- 


Surface  aspect. 


Lateral  aspect. 


Section  of  the  border  of  a  cell,  with  the  nu- 
clei!': uncut. 


Lacunae.        Canahculi  in 
cross-section. 


Canaliculi. 


Nucleus.     Protoplasm.        Lacuna. 
£one-cell. 


Fig.  47. — Portion  of  a  Ground  Section  of  the  Infe-       Fig.  48.— Section  of  the  Osseous  Tur- 
RiOR  Maxill.a  of  Adult  NLan.     x  550.    Technic  No.  binal  of  Adult  Man.    X  550.    Tech- 

61.  nic  No.  63. 


Bone-matrix. 


Osteoblasts. 


Bone-cell. 


Osteoblast  changing 
to  a  bone-cell. 


>    t' 


Fig.  49. — Portion  of  a  Cross-section  of  the  Diaphysis  of  the  Hu.merus  of  a  Hu.m.-\n  Embryo 
Four  Months  Old.    X  560.    Technic  No.  67. 


ful  whether  in  the  adult  the  bone-cells  are  connected  by  means  of  pro- 
cesses extending  through  the  canaliculi,  although  such  connection  is 
readily  observed  in  developing  bone  (Fig.  49). 


lOO  HISTOLOGY. 

Usually  the  formation  of  osseous  tissue  takes  place  in  such  a  way 
that  the  ground  substance  of  the  connective  tissue  or  of  the  cartilage 
calcifies  during  embryonic  life.  Around  the  trabeculae  of  the  calcified 
matrix  numerous  young,  still  indifferent,  connective-tissue  cells  then 
arrange  themselves,  which  produce  the  at  first  soft,  then  calcified 
ground  substance  of  bone.  These  cells  are  called  osteoblasts.  At  first 
they  lie  upon  the  osseous  matrix  they  have  formed,  later  they  come  to 
lie  within  it,  and  gradually,  by  development  of  processes,  become  trans- 
formed into  stellate  bone-cells.* 

Dentine  is  a  modification  of  bone,  from  which  it  is  distinguished  by 
its  developmental  history  and  in  the  fact  that  the  formative  cells,  the 
odontoblasts,  are  not  enclosed  within  the  matrix,  but  penetrate  the  latter 
only  with  their  processes.  Further  details  will  be  found  in  connection 
with  the  structure  of  teeth. 

THE    BLOOD-VESSELS,    LYMPH- VESSELS,    AND    NERVES    OF    THE 
SUPPORTING    TISSUES. 

The  organs  formed  of  supporting  tissue  are,  in  general,  poorly 
supplied  with  blood-vessels,t  lymph-vessels,  and  nerves.  But  supporting 
tissue  plays  a  very  important  part  as  a  conveying  apparatus  in  the  trans- 
ference of  nutritive  fluids — tissue-Juice,  lymph — from  the  blood-vessels  to 
the  tissues.  It  moves  in  the  ground  substance  and  when  this  is  soft,  as 
in  mucous  and  loose  connective  tissue,  the  lymph  permeates  the  entire 
mass ;  when  on  the  other  hand  the  ground  substance  is  denser,  the 
lymph  circulates  in  definite  channels,  in  d^  juice-canal-system  formed  by  the 
cell-spaces,  the  lymph-spaces,  and  the  minute  canals  connecting  them,  the 
lymph  canaliculi  (cf.  the  cornea).  This  is  the  case  in  the  more  compact 
connective  tissues  %  and  in  bone.  Whether  the  tissue-juice  is  diffused 
throughout  the  matrix  of  hyaline  cartilage  or  conveyed  in  definite  chan- 
nels is  still  undetermined. 


*  Direct  transmutation  of  developed  connective  tissue  or  cartilage  into  osseous  tissue 
does  not  occur.  The  processes  collectively  designated  "metaplasia"  are  much  better  inter- 
preted as  signifying  that  indifferent  formative  cells  of  connective  tissue,  subject  to  dissimilar 
influences,  may  develop,  now  into  bone-cells,  now  into  cartilage-cells,  or  into  typical  tendon 
cells  (see  also  the  chapter  on  Development  of  Bone). 

f  Adipose  tissue  forms  an  exception. 

X  The  lymph  canaliculi  occurring  here  stand  in  direct  connection  with  the  intercellular 
clefts  of  the  epithelial  tissues,  which  we  must  imagine  as  similarly  permeated  by  the  tissue 
juice. 


THE     TISSUES.  lOI 


TECHNIC. 


No.  4. — Mucous  connective  tissue. — Place  the  umbilical  cord  of  a 
human  embryo  of  three  or  four  months  (or  pig  embryo  from  three  to 
six  cm.  long)  in  50  c.c.  of  Zenker's  fluid  (p.  33)  for  24  hours;  harden 
in  30  c.c.  of  gradually  strengthened  alcohols  (p.  35).  The  cord  will 
still  be  very  soft ;  in  order  to  obtain  good  sections  it  must  be  embedded 
in  liver,  and  in  cutting  must  be  somewhat  compressed  with  the  fingers. 
The  sections  may  be  stained  in  picrocarmine  (twelve  hours)  or  in  Han- 
sen's hematoxylin  (five  minutes),  and  should  be  examined  in  a  drop  of 
distilled  water  (Fig.  33).  In  glycerol  and  in  xylol-balsam  the  delicate 
processes  of  the  cells  and  the  bundles  of  connective  tissues  are  invisible. 
In  the  vicinity  of  the  blood-vessels  the  network  of  cells  is  less  fine  ; 
therefore  a  field  remote  from  the  blood-vessels  should  be  selected  for 
study.  The  older  the  embryo,  the  greater  is  the  number  of  connec- 
tive-tissue bundles.      Mount  in  diluted  glycerol  (p.  49). 

No.  5. — Fibrillar  connective  tissue;  connective-tisstie  bundles. — 
Prepare  small  strips,  one  or  two  cm.  long,  of  intermuscular  connective  tis- 
sue, for  example,  of  the  thin  septum  between  the  serratus  and  the  intercos- 
tal muscles  ;  place  a  small  piece  on  a  dry  slide  and  quickly  spread  it  out 
with  teasing  needles  (see  "half-drying  method"  No.  31  ^r,  p.  123),  add 
a  drop  of  salt  solution  and  apply  a  cover-glass.  The  bundles  of  con- 
nective tissue  appear  wa\y  and  pale  (Fig.  34)  ;  with  a  little  practice  the 
sharply  contoured,  highly  refracting  elastic  fibers  can  be  distinguished 
and  also,  in  favorable  situations,  the  nuclei  of  the  connective-tissue  cells. 

No.  6. — The  cells  of  fibrillar  connective  tissiie  may  be  made  visi- 
ble by  the  addition  of  a  drop  of  picrocarmine  to  preparation  No.  5,  under 
the  cover-glass  (p.  53).  In  most  cases  only  the  red  nucleus  can  be  per- 
ceived, especially  when  the  cell  lies  wholly  upon  the  connective-tissue 
bundle.  In  rare  cases  the  pale  yellow,  variously  shaped  body  of  the  cell 
can  be  seen  (Fig.  Z7  ^'^'  ^  ^^<^  -)• 

No.  7. — Mast-cells. — Fix  small  pieces,  i  or  2  cm.  square,  of  mucous 
membrane  (of  the  mouth,  pharynx,  or  intestine)  in  ninety-five  per  cent, 
alcohol  (p.  31).  In  from  three  to  eight  days  cut  thin  sections  and  stain 
them  in  10  c.c.  of  alum-carmine  dahlia  for  twenty-four  hours  (p.  26). 
Transfer  them  to  10  c.c.  of  absolute  alcohol  for  twenty-four  hours,  which 
must  be  renewed  once  or  twice  during  this  time.  Mount  in  xylol-balsam 
(p.  50).  The  protoplasm  of  the  mast-cells  exhibits  granules  stained  an 
intense  blue. 

No.  8. — FibrillcB. — Place  a  piece  of  tendon  about  2  cm.  long  in  100 
c.c.  of  saturated  aqueous  solution  of  picric  acid.  On  the  following  day, 
with  two  pairs  of  forceps,  pull  the  tendon  apart  along  its  length,  take 
from  the  interior  a  bundle  about  5  mm.  long,  and  tease  the  same  on  a 
dr)'  slide  {cf.  No.  31  «,  p.   123)  ;  add  a  drop  of  distilled  water,  apply  a 


I02 


HISTOLOGY. 


cover-glass,  and  examine  with  the  high-power  objective, 
fibrillae  appear  as  exceedingly  fine,  pale  filaments. 


The  ultimate 


No.  9. — Encircling  fibers. — With  the  scissors  cut  out  a  piece  about 
one  cm.  square  of  the  connective  tissue  within  the  arterial  circle  of  Willis, 
wash  it  in  a  watch-glass  with  salt  solution,  with  needles  spread  it  out 
in  a  drop  of  the  same  solution  on  a  slide,  and  cover.  With  the  low  power, 
in  addition  to  numerous  delicate  blood-vessels  and  ordinary  connective- 
tissue  bundles,  sharply  contoured,  refracting  bundles,  in  distinct  contrast 
to  the  remaining  connective  tissue,  will  be  found,  which  on  the  use  of 
the  high  power,  and  a  diaphragm  of  narrow  aperture,  show  that  they  like- 
wise consist  of  fibrillar  connective  tissue.  Place  such  a  bundle  in  the 
field  and  treat  it  with  a  drop  of  acetic  acid,  under  the  cover-glass  (p.  53). 
So  soon  as  the  acid  reaches  the  bundle,  it  swells,  the  fibrillation  vanishes 
and  instead  elongated  nuclei  appear.  The  swelling  is  not  uniform  ;  at 
irregular  intervals  the  bundle  is  constricted.      With  dim  illumination  the 


Fat-cells  in  a 
simple  layer  ; 


in  superposed 
layers. 


Fibrillar  con- 
nective tissue. 


Fig.  50. — Adipose  Tissue  FROM  A  Section  OF  Human  Scalp.      X  50.    Technic  No.  i6i.      Cy.  Technic 

No.  II. 


"  fibers  "  Tcell-remnants)  producing  the  constrictions  can  be  seen  (Fig. 
37  B). 

No.  10. — Fat-cells. — Take  a  small  piece  of  the  reddish-yellow, 
gelatinous  fat  from  the  axilla  of  a  thoroughly  emaciated  individual ; 
rapidly  spread  out  a  piece  the  size  of  a  split  pea  in  the  thinnest  possible 
layer  on  a  dry  slide,  immediately  add  a  drop  of  salt  solution  and  apply  a 
cover-glass.  In  thin  places  atrophic  fat-cells,  like  those  shown  in  figure 
40,  will  be  seen.  This  preparation  may  be  stained  under  the  cover- 
glass  with  picrocarmine  (p.  53)  and  preserved  in  diluted  glycerol.  Ordi- 
nary (normal)  fat-cells,  taken  from  any  part  of  the  body,  are  likewise  to 
be  examined  in  salt  solution.  The  spherical  cells  should  be  studied  with 
change  of  focus  {cf.  Fig.  38). 

No.  II. — Adipose  tissue  may  be  seen  in  sections  of  many  prepara- 
tions fixed  by  any  of  the  usual  methods,  above  all  of  the  skin  {cf.  Fig. 


THE     TISSUES.  IO3 

288).  The  oily  contents  are  withdrawn  by  the  treatment  with  alcohol 
and  then  the  clusters  of  empty  cell-envelopes  present  a  picture  that  the 
beginner  often  finds  difficulty  in  understanding  (Fig.  50). 

No.  12. — Fine  elastic  fibers  may  be  readily  obtained  by  treating 
preparation  No.  5,  under  the  cover-glass,  with  a  few  drops  of  acetic  acid. 
The  connective-tissue  bundles  swell  and  become  transparent ;  the  elastic 
fibers,  on  the  contrary,  remain  unaltered  and  stand  out  sharply  con- 
toured (Fig.  35  A). 

No.  13. — T/uck  clastic  fibers  may  be  obtained  by  teasing  in  a  drop 
of  salt  solution  a  slender  piece,  about  5  mm.  long,  of  the  fresh  ligamen- 
tum  nuchse  of  an  ox  (Fig.  35  B).  The  piece  should  not  be  taken  from 
the  loose,  enveloping  tissue,  but  from  the  tough,  yellowish,  fibrous  por- 
tion. The  preparation  may  be  stained  in  picrocarmine  (p.  41)  and 
mounted  in  glycerol. 

No.  14. — Cross-sections  of  thick  elastic  fibers  may  be  obtained  by 
drying  a  piece  (10  cm.  long  and  from  i  to  2  cm.  thick)  of  the  ligamentum 
nuchae  (it  will  be  ready  to  use  in  four  or  six  days)  and  treating  it  like 
No.  69. 

No.  15. — Fenestrated  membranes. — Take  a  small  piece  (about  5  mm. 
square)  of  the  endocardium,  place  it  in  a  drop  of  water  on  a  slide  and 
add,  under  the  cover-glass,  i  or  2  drops  of  potash-lye.  Examine  the 
edges  of  the  preparation  (Fig.  36). 

Good  specimens  may  also  be  obtained  from  the  basilar  artery  ;  place 
a  piece  of  the  artery  cut  open  lengthwise  in  10  c.c.  of  concentrated 
potash  solution.  After  six  hours  take  a  small  piece,  about  i  cm.  long, 
and  separate  the  lamellae  in  a  drop  of  water  on  a  slide  ;  this  is  easily 
done  by  scraping  with  a  scalpel.  Cover  and  examine  with  the  high 
power.  The  small  holes  in  the  membrane  have  the  appearance  of  shining 
nuclei.  With  the  low  power  the  membrane  is  recognized  by  its  dark  out- 
lines. To  preserve,  wash  it  well  in  10  c.c.  of  water  for  five  minutes,  stain  it 
in  3  c.c.  of  congo-red  for  from  twelve  to  twenty  hours  (p.  25),  and  mount 
in  xylol-balsam  (p.  50). 

No.  16. — A  netzvork  of  connective-tissue  bundles  maybe  obtained  by 
spreading  out  a  little  piece  of  fresh  human  omentum  in  a  few  drops  of 
picrocarmine.  It  ma^  be  preserved  in  diluted,  nonacidulated  glycerol 
(p.  49).  Pieces  of  the  omentum  fixed  in  absolute  alcohol  and  stained 
with  hematoxylin  and  eosin  (p.  39)  may  be  mounted  in  xylol-balsam 
(p.  50).      (Fig.  41,  p.  94.) 

No.  17. — Hyaline  cartilage. — Cut  off  the  extremely  thin  episternum 
of  the  frog,  place  it  on  a  dry  slide,  cover  it  with  a  cover-glass,  and 
examine  at  once  with  the  high  power.  The  cartilage  cells  completely 
fill  the  cartilage  cavities  (Fig.  43).  For  prolonged  study  add  a  drop  of 
saline  solution. 


I04  HISTOLOGY. 

No.  1 8. — Hyaline  costal  cartilage. — ^Without  any  previous  prepara- 
tion thin  sections  of  costal  cartilage  may  be  cut  with  a  razor  and 
examined  in  a  drop  of  water  under  a  cover-glass.  Search  for  one  of  the 
glossy  areas  containing  rigid  fibers  (Fig.  44).  The  preparation  may 
be  preser\'ed  by  adding  a  few  drops  of  dilute  glycerol. 

Fresh  cartilage  does  not  readily  stain.  The  tissue  must  be  first 
placed  in  Zenker's  or  in  ]\Iuller's  fluid  (p.  33),  then  in  alcohol  (p.  35), 
and  subsequently  stained  with  Hansen's  hematoxylin  (p.  38).  Mounted 
in  x}-lol-balsam,  which  clears  vigorously,  the  finer  details  vanish. 

No.  19. — Elastic  cartilage. — Take  a  piece  of  the  arytenoid  cartilage 
of  man  (better  still  of  the  ox),  the  elastic  cartilage  of  the  apex  and  the 
vocal  process  is  recognized  by  its  yellowish  color.  Cut  a  section  that 
includes  the  boundary  line  between  the  elastic  and  the  hyaline  cartilage  and 
examine  it  in  water.  Preserve  like  No.  18.  The  development  of  elastic 
fibers  may  often  be  studied  in  the  cartilages  of  adults,  especially  in  the 
epiglottis  and  in  the  vocal  process  of  the  arytenoid  cartilage  (Fig.  45,  i). 
See  also  Technic  Xo.  128. 

No.  20. — Fibrous  cartilage. — Cut  the  intervertebral  disks  of  adult 
man  in  pieces  from  i  to  2  cm.  square  ;  fix  in  100  c.c.  of  potassium- 
bichromate-acetic  acid  (p.  32)  for  twenty -four  hours  and  harden  in  50 
c.c.  of  gradually  strengthened  alcohols  (p.  35).  Stain  sections  in  Han- 
sen's hematoxylin  (p.  38)  and  mount  in  balsam  (Fig.  46).  Sections 
through  the  edges  yield  hyaline  cartilage  ;  through  the  central  portions 
of  the  disk  they  exhibit  large  groups  of  cartilage-cells. 


in.    THE    MUSCLE   TISSUES. 

The  characteristic  elements  of  the  muscle  tissues,  the  vmscle-fibers, 
occur  in  two  forms,  named  the  smootli  and  the  striated.  Both  are  cells, 
the  body  of  which  is  extraordinarily  elongated. 

I.  Smooth,  nonstriated  m'  involuntary  muscle. — The  tissue  of  smooth 
muscle  consists  of  contractile  fiber-cells,  spindle-shaped,  cylindric,  or 
slightly  flattened  elements  with  tapering  extremities  (Fig.  51).  Their 
length  in  man  varies  from  45  to  225  a,  their  width  from  4  to  7  a  ;  in  the 
gravid  uterus  smooth  muscle-fibers  measuring  0.5  mm.  have  been  found. 
They  consist  of  a  delicately  striated  protoplasm — the  striations  indicate 
that  the  fiber  is  composed  of  fibrillae — and  an  elongated,  elliptical,  or 
rod-shaped  nucleus,  that  is  characteristic  of  the  smooth  muscle-fiber.* 

The  smooth  muscle-fibers  sometimes  lie  scattered  in  the  connective 
tissue,  sometimes   are  intimately  united   in   complexes,  by  delicate,  per- 

*The  diplosome  lies  on  the  longitudinal  side  of  the  somewhat  eccentrically  situated 
nucleus.  Smooth  muscle-fibers  containing  pigment  have  been  found  in  the  iris  of  fishes  and 
amphibians,  also  in  the  human  intestine  and  iris  (dilatator  pupillse). 


THE     TISSUES. 


lO: 


forated  connective-tissue  membranes.*  The  development  of  these  mem- 
branes varies  greatly  ;  while,  for  example,  they  are  very  tender  in  the 
musculature  of  the  intestinal  wall,  so  that  their  demonstration  is  possible 
only  by  certain  methods,  between  the  muscle-fibers  of  the  ureter  and 
yet  more  between  those  of  the  oviduct  they  are  so  well  developed,  that 
in  specific  connective-tissue  staining  the  muscles  are  completely  hidden. 
Thicker  connective-tissue  septa  occur  only  at  wide  intervals  (Fig.  52)  ; 
elastic  fibers  are  present,  as  well  in  the  thicker  septa  as  in  the  delicate 
membranes. 


Fig.  51. — Two  Smooth  Muscle-fibers  from  the  Small  Intestine  of  a  Frog.  X  240.  Isolated  in  55 
per  cent,  potash-lye.  The  nuclei  have  lost  their  characteristic  form  through  the  action  of  the  lye. 
Technic  No.  21  a. 


Connective-tissue  _ 
septum. 


Smooth  muscle-fibersi 
and  nuclei  in  trans-  > 
verse  section.  J 


The  union  of  the  complexes  results  either  in  membranes,  in  which 
their  disposition  is  parallel,  as  in  the  muscle  of  the  intestine,  or  in  com- 
plicated networks,  as  in  the  urinary  bladder  and  the  uterus.  The  larger 
blood-vessels  run  in  the  stout  connecti\'e-tissue  septa,  but  the  capil- 
laries penetrate  between  the  muscle-fibers  and  form  longitudinal  net- 
works. The  lymph-vessels  follow 
the  course  of  the  blood-vessels  and 
are  present  in  conspicuous  number. 
■  For  the  nerves  of  smooth 
muscle,  see  the  Peripheral  Nerve- 
endings. 

Smooth  muscle-tissue  occurs 
in  the  alimentary  canal,  in  the 
trachea  and  bronchial  tubes,  in  the 
gall-bladder,  in  the  pelvis  of  the 
kidneys,  in  the  ureters  and  the  uri- 
nary bladder,  in  the  reproductive  organs,  in  the  blood-  and  lymph-ves- 
sels, in  the  eye,  and  in  the  skin.  The  contraction  of  smooth  muscle- 
fiber  is  slow  and  not  under  the  control  of  the  will. 

The  musculature  of  the  heart  occupies  a  peculiar  position.  In  the 
lower  vertebrates,  in  frogs,  for  example,  the  cardiac  muscle-fibers  are 
spindle-shaped  elements  possessing  elliptical  nuclei,  and  often  are  more 
distinctly  striated  transversely  than  longitudinally  (Fig.  53  A). 

Fibers  can  also  be  isolated  in  mammals  ;  short  cylinders,  which 
often  have  step-like  ends  (Fig.  53  B).     The  protoplasm  is  partially  dif- 


FiG.  52. — Section  of  the  Circular  Muscle 
Coat  of  the  Human  Intestine.  X  500. 
The  membranes  are  not  visible  here,  so  that 
the  muscle-fibers  appear  to  be  in  contact  with 
one  another.     Technic  No.  iii. 


*  Regarding  the  intercellular  bridges,  see  Technic  No.  21  b. 


io6 


HISTOLOGY. 


ferentiated  into  cross-striated  fibrils,  fibrillcE,  which  not  infrequently  are 
arranged  in  lamellae  radially  placed  to  the  axis  of  the  fiber  (Fig.  53  D). 
The  remnant  of  undifferentiated  protoplasm,  the  sarcoplasin,  relatively 
considerable  in  comparison  with  that  of  striated  muscles,  is  found  chiefly 
in  the  axial  part  of  the  fiber,  from  which  processes  radiate  between  the 
lamellae.  Owing  to  this  longitudinal  striation  is  often  v^txy  marked. 
The  oval  nucleus  is  embedded  in  the  axial  part  of  the  sarcoplasm,  which 
very  frequently  contains  granules  of  pigment  or  fat.  A  membrane 
equivalent  to  the  sarcolemma  of  striated  muscle-fibers  is  wanting.  Char- 
acteristic of  the  cardiac  muscle-fibers  of  higher  animals  is  the  union  of 
the  fibers  by  means  of  short  oblique  or  transverse  processes  (Fig.  53  B  x). 
According  to  recent  investigations  these  cardiac  muscle-fibers  are 
artifacts,  fragments  of  a  protoplasmic  net  provided  with  nuclei,  a  syncyt- 


Sarcoplasm. 


Fig.  53.— /4  and  ^,  Cardiac  Muscle-fibers,  isolated  in  potash-lye.  yl.ofthe  frog;  B,oi  the  rabbit; 
X,  oblique  branch.  X  240.  Technic  like  No.  26.  C,  from  a  longitudinal  section,  D,  from  a  cross- 
section  of  a  papillary  muscle  of  man.     C magnified  240,  D  560  diameters.    Technic  No.  37. 


ium,  that  is  already  present  in  early  epochs  of  developmental  history. 
The  transverse  lines  ("cement-lines"),  often  distinct  in  longitudinal  sec- 
tions, the  significance  of  which  is  not  yet  satisfactorily  explained,  are  said 
to  be  not  cell  or  muscle-fiber  boundaries,  because  they  are  pierced  by 
the  muscle  fibrillae  {cf.  Union  of  cells,  p.  73). 

2.  Striated  or  voluntary  nmscle. — It  is  only  by  the  study  of  their 
development  that  the  striated  muscle-fibers  are  recognized  as  cells.  By 
a  colossal  growth  in  length,  by  repeated  division  of  their  nuclei,  as  well 
as  by  peculiar  differentiation  of  their  protoplasm,  they  have  become 
highly  complicated  structures.  They  have  the  form  of  long  cylindrical 
threads,  the  ends  of  which,  in  the  interior  of  the  larger  muscles,  are 
rounded  or  pointed  ;  at  the  extremities  of  the  muscle  they  possess  a 
pointed  inner  end  and  a  broader  end  in  contact  with  the  tendon  ;  the 
latter  is  either  blunt  or   terminates   in   several   stumpy,    often    steplike 


THE     TISSUES. 


107 


notches.  Anastomoses,  divisions,  and  fissures  occur  ;  branched  fibers 
are  found  in  the  muscles  of  the  eye,  the  tongue,  and  the  skin  (Fig.  56,  4). 
They  vary  in  length  from  5.3  to  12.3  cm.,*  in  thickness  from  10  to 
100  II.  In  the  embryonal  body  no  difference,  or  only  an  insignificant 
difference  in  thickness  exists  ;  after  birth  an  unequal  growth  in  the  thick- 
ness of  the  muscle-fibers  takes  place,  the  intensity  of  which  is  dependent 
on  :  (i)  the  function  of  the  muscle  ;  in  the  adult  robust  muscles  possess 
thick  fibers,  delicate  muscles  have  thin  fibers  ;  (2)  the  nutritional  con- 
dition of  the  individual ;  (3)  the  size  of  the  animal,  large  animals  possess 
thicker  fibers  than  smaller  ones.  Hence  the  difference  in  caliber  may 
be  of  a  threefold  nature. 

Under   the    microscope    each    cross-striated    muscle-fiber    exhibits 
alternate  broad  dim  and  narrower  clear  transverse  stripes.    The  substance 


B 


<f 


Fig.  54. — B.  Portion  of  a  Muscle-fiber  of  Man  ;  a,  anisotropic,  /,  isotropic  band :  q,  intermediate 
disk;  /t,  nucleus.  X  560.  Technic  No.  22  *.  ^.  Muscle-fiber  of  a  Frog  ;/,  fibrillse;  ^,  nucleus. 
X  240.    Technic  No.  25. 


of  the  dim  stripes  is  doubly  refracting  or  anisotropic,  that  of  the  clear 
stripes  singly  refracting  or  isotropic.^  Besides  the  cross-marking,  a  more 
or  less  distinct  longitudinal  striation  may  be  observed.  Treatment  with 
certain  reagents  {e.  g.  solution  of  chromic  acid)  renders  this  striation  more 
evident  and  even  causes  the  muscle-fiber  to  fall  apart  longitudinally  in 
delicate,  likewise  cross-striped,  filaments,  which  are  cdAled  Jibrillce.    These 


*  It  is  probable  that  there  are  fibers  having  greater  length,  but  their  isolation  entire  is  very 
difficult  to  accomplish. 

I  High  amplifications  show  that  each  transverse  disk  is  transversely  divided  ;  invariably  in 
the  isotropic  (clear)  zone  a  dim  line  occurs,  the  intermediate  disk  (Fig.  54)  ?)>  and  above  and 
below  this  a  dark  band,  the  accessory  disk.  In  the  anisotropic  (dim)  band  a  clear  stripe,  the 
tnedian  disk,  has  been  observed.  Owing  to  their  extreme  variation  and  t^ieir  instability,  these 
disks  are  of  subordinate  significance. 


io8 


HISTOLOGY. 


fibrillae  are  the  contractile  structural  elements  of  the  muscle-fiber.*     They 
are  grouped  into  longitudinal  bundles,  the  muscle-columns ,  in  which  they 


•^^         Blood  capil- 
laries. 


Bundles  of  fibrillae  (Cohn- 
heim's  fields). 


Perimysium  of  the  individual  muscle-fiber. 

Fig.  55.— From  a  Cross-section  of  the  Arytenoid  Muscle  of  Man.    Four  muscle-fibers  are  repre- 
sented.    X  590.     Technic  No.  128. 

are  arranged  parallel  to  one  another  and  held  together  by  the  sarcoplasm, 
which  also  unites  them  with  neighboring  bundles.     The  disposition  of  the 


.y  -4 


Fig.  56. — Portions  of  Isolated  Striated  Muscle-fibers  of  a  Frog.  X  50.  i.  After  treatment  with 
water :  j,  s^,  sarcolemma ;  at  x  the  muscle-substance  is  torn,  the  cross-striation  not  apparent,  the  longi- 
tudinal striation  distinct.  Technic  No.  23.  2.  After  treatment  with  acetic  acid:  /^,  nuclei;  the  fine 
stippling  represents  the  interstitial  granules.  Technic  No.  24.  3.  After  the  action  of  concentrated 
potash  solution  :  e,  rounded  ends  ;  the  numerous  nuclei  are  swollen  and  vesicular  in  appearance. 
With  this  amplification  the  cross-striation  in  2  and  3  is  invisible.  Technic  No.  26.  4.  Branched 
muscle-fiber  from  the  tongue  of  a  frog.     Technic  No.  27. 

sarcoplasm  is  best  seen  in  cross-section  ;  high  amplification  is  required. 
It  presents  the  appearance  of  a  clear  network,  within  the  meshes  of  which 


*The  muscle-fibers  of  some  animals,  after  treatment  with  certain  reagents,  cleave  trans- 
versely into  disks.  Fibrillae  and  disks  may  be  further  separated  into  smaller,  polygonal,  aniso- 
tropic particles,  that  were  called  sarcous  elements.  Certain  authors  interpreted  the  disks,  others 
the  sarcous  elements,  as  the  true  structural  units. 


THE     TISSUES.  IO9 

are  the  muscle-columns  in  section,  known  as  CoJuiJiciin  s  fields  (Fig.  55). 
The  sarcoplasm  contains  the  interstitial  granules,  consisting  partly  of  fat 
and  probably  also  of  lecithin,  and  the  nuclei.  The  latter  are  oval  bodies 
placed  parallel  to  the  long  axis  of  the  muscle-fiber  ;  in  mammals,  bony 
fishes,  and  some  birds  they  are  chiefly  situated  upon  the  surface  of  the 
muscle-fiber,  beneath  the  sarcolemma  ;  in  other  vertebrates  they  lie  also 
in  the  interior  of  the  fiber.*  The  number  of  the  nuclei  is  from  3  to  12 
times  greater  in  thin  than  in  thick  muscle-fibers. 

Each  muscle-fiber  is  snugly  enclosed  in  a  structureless  sheath,  the 
sarcolemma,  which  represents  the  cell-membrane.  Therefore  the  fiber 
of  striated  muscle  consists  of  fibrillse,  sarcoplasm,  nuclei,  and  sarco- 
lemma. 

The  striated  fibers  are  found  in  the  muscles  of  the  trunk  and  the 
extremities,  of  the  eye  and  the  ear,  also  in  the  tongue,  the  pharynx,  the 
upper  half  of  the  esophagus,  the  larynx,  the  diaphragm,  the  genital 
organs,  and  the  rectum. 

In  some  animals,  the  rabbit,  for  exam^ple,  two  varieties  of  striated 
muscles  are  distinguished,  the  red  {e.  g.  the  semitendinosus,  the  soleus) 
and  the  zvliite  or  pale  {e.  g.  the  adductor  magnus)  ;  and  correspondingly, 
two  varieties  of  muscle-fibers  :  (i)  dim  fibers,  ricJi  in  protoplasm,  or  sar- 
coplasm, showing  less  regular  cross-striation,  more  distinct  longitudinal 
striation,  possessing  in  general  a  smaller  diameter  (for  example,  those 
forming  the  red  soleus  of  the  rabbit)  ;  (2)  pale  fibers, /(^cr  i)i  protoplasm, 
more  distinctly  cross-striated  and  having  in  general  a  greater  diameter. 
The  latter  represent  the  more  highly  differentiated  muscle-fibers.  While 
in  certain  animals  the  two  varieties  of  fibers  occur  separately,  each  in 
particular  muscles,  in  others — also  in  man — they  are  found  intermingled 
in  the  same  muscle.  As  a  rule,  the  more  functionally  active  muscles, 
the  cardiac,  ocular,  masticatory,  and  respiratory,  contain  the  greater 
number  of  fibers  rich  in  protoplasm.  The  muscles  with  many  pale  fibers 
contract  more  rapidly,  but  are  sooner  fatigued. 

The  contraction  of  the  striated  fibers,  compared  with  that  of  smooth 
muscle-fibers,  is  rapid  and  is  under  the  control  of  the  will.  The  striated 
fibers  are  united  into  bundles  by  fibrillar  connective  tissue,  which  serves 
also  to  convey  the  numerous  ramifications  of  the  blood-vessels  and 
nerves  supplying  the  muscle  tissue.  The  lymph-vessels  are  few  in 
number. 

*In  man,  also,  nuclei  occur  in  the  interior  of  the  muscle-fiber  and  especially  well  devel- 
oped in  the  neighborhood  of  the  insertion  of  the  tendon,  thin  and  stunted  in  the  rest  of  the 
muscle  substance.  The  nuclei  at  the  ends  of  the  muscle-fibers,  often  numerous  and  arising  by 
amitotic  division,  indicate  that  these  are  the  places  where  the  growth  in  the  length  of  the  fibers 
occurs. 


no 


HISTOLOGY. 


TECHNIC. 

No.  21. — Smooth  muscle-fibers  {a)  isolated. — These  are  best  ob- 
tained by  treating  a  little  piece  of  the  stomach  or  intestine  of  a  frog 
just  killed  with  20c.c.  of  potash  lye.  Cover  the  glass.  After  from  30 
to  60  minutes  (in  a  cold  room  somewhat  later),  the  intestine  falls  to 
pieces  on  being  slightly  stirred  with  a  glass  rod.  If  the  action  fails  the 
lye  is  not  strong  enough  (see  p.  30).  Transfer  a  drop  containing  some 
of  the  sediment  to  a  sHde  (the  fibers  cannot  be  examined  in  water  or 
glycerol,  for  the  lye  thus  diluted  will  immediately  destroy  them)  ;  care- 
fully apply  a  cover-glass  and  examine  with  the  high  power  (Fig.  51). 

After  treating  small  pieces  of  intestine  with  100  c.c.  of  Miiller's 
fluid  ^(p.  21)  for  from  8  to  14  days  smooth  muscle-fibers  can  be  isolated 
by  teasing,  but  successful  preparations  are  difficult  to  obtain  from 
the  intestine  of  man  and  also  of  the  frog,  easier  on  the  other  hand  from 
that  of  the  horse  (take  the  lower  portion  of  the  duodenum)  and  also  of 
the  rat. 


)^' 


End  of  a  muscle-fiber. 


Nerve-cell. 


Fig.  57. — Apparent  Intercellular  Bridges  of  Smooth  Muscle-fibers.    A.  Transverse  section  of 
the  intestine  of  a  rabbit.     B.  Longitudinal  section  of  the  intestine  of  a  guinea-pig.     >(  420. 


(U)  Cross-sections  of  bundles  of  smooth  mnscle  fibers. — Many  fixation 
fluids  cause  shrinking  of  the  fibers,  which  gives  rise  to  deceptive  pic- 
tures ;  such  are  the  intercellidar  bridges.  Pictures  like  that  of  Fig.  57 
can  often  be  obtained  in  very  thin  sections  of  tissue  (pieces  from  i  to  2 
cm.  long  of  the  small  intestine  of  a  guinea-pig  or  rabbit y^/i-^"  killed)  fixed 
in  100  c.c.  of  Zenker's  fluid  (p.  33)  and  hardened  in  gradually  strength- 
ened alcohols  (p.  35). 

The  twisted  nuclei  of  smooth  muscle-fibers  also  belong  in  the  cate- 
gory of  artifacts. 

The  demonstration  of  the  connective-tissue  membrane  enveloping 
each  individual  muscle-fiber  succeeds  only  by  special  staining  (van  Gie- 
son,  p.  43) ;  the  sections  must  not  be  thinner  than  10  p.. 

No.  22. — Striated  muscle  fibers  id)  of  the  f'og. — With  the  scissors 
placed  flat  and  parallel  to  the  course  of  the  fibers,  cut  a  piece  about  i 
cm.  long  from  the  adductor  muscle  of  a  recently  killed  frog.  Take  a 
fragment  from  the  inner  surface  of  this  piece  and  tease  it  in  a  small  drop 


THE     TISSUES.  •  III 

of  salt  solution  (see  Isolation,  p.  29),  add  a  second  larger  drop  of  the 
same  liquid  and,  witJioiit  pressing,  cover  the  preparation  with  a  cover- 
glass.  With  low  magnification  (50  diameters)  the  cylindrical  form,  the 
difference  in  thickness,  occasionally  also  the  cross-striation  of  the  isolated 
fibers  can  be  seen  (Fig.  56).  With  higher  magnification  (240  diame- 
ters) the  cross-striation  is  distinctly  seen  and  occasionally  pale  nuclei  and 
refracting  granules.  The  presence  of  numerous  granules  within  the 
muscle-fibers  is  probably  an  indication  of  active  metabolic  processes. 
Where  the  muscle-fibers  are  cut  across,  the  muscle-substance  not  infre- 
quently protrudes  from  the  sarcolemma, 

(b)  Of  man. — I  have  found  beautiful  striated  fibers  in  muscles  taken 
from  the  human  cadaver  injected  with  carbolic  acid.  To  preserve,  stain 
under  the  cover-glass  with  picrocarmine  (p.  53)  for  about  five  minutes, 
then  displace  the  staining  fl^uid  with  diluted  glycerol. 

No.  23. —  The  sarcolemma. — Treat  preparation  No.  22  a  with  a 
couple  of  drops  of  ordinary  water.  In  from  two  to  five  minutes  it  will 
be  seen,  with  the  low  power  (50  diameters),  that  the  sarcolemma  is 
raised  from  the  muscle-substance  in  the  form  of  transparent  vesicles  ;  at 
some  places,  where  the  torn  muscle-substance  has  retracted,  the  sheath 
appears  as  a  delicate  line  spanning  the  interval  (Fig.  56,  i,  s  s'). 

No.  24. — Muscle  nuclei. — Prepare  muscle-fibers  after  No.  22  a; 
treat  them  with  a  drop  of  acetic  acid  (p.  53).  The  shrunken  but 
sharply  outlined  nuclei,  with  the  lower  power,  have  the  appearance  of 
dark,  spindle-shaped  streaks  (Fig.  56,  3). 

No.  25. — Fibrillcs. — Place  a  fresh  muscle  of  a  frog  in  20  c.c.  of 
0.1  percent,  chromic-acid  solution  (p.  21).  In  about  twenty-four  hours 
the  tissue  can  be  teased  in  a  drop  of  water  and  fibers  will  be  found,  the 
ends  of  which  have  separated  into  fibrillae  (Fig.  54,  A).  If  it  is  desired 
to  make  a  permanent  preparation,  place  the  muscle  in  water  for  one 
hour,  then  in  20  c.c.  of  33  per  cent.  alcohol,^ten  or  twenty  hours  ;  tease 
at  once  or  preserve  in  70  per  cent,  alcohol  until  wanted  and  then  isolate 
(p.  29).  If  the  chromic  acid  be  removed  by  allowing  the  tissue  to  remain 
in  alcohol  (frequently  renewed)  for  several  weeks,  the  teased  preparation 
may  then  be  stained  with  picrocarmine  in  the  moist  chamber  and  this 
replaced  by  glycerol  (p.  53).  Beautiful  fibrillse  can  also  be  obtained  by 
teasing  the  muscles  of  larval  salamanders  that  have  been  fixed  according 
to  technic  No.  i  and  stained  in  bulk  in  borax-carmine  (p.  40).  Pieces 
of  such  muscle  are  transferred  from  absolute  alcohol  to  carbol-xylol 
and  teased  on  a  slide  in  a  drop  of  the  latter.  Examine  with  the  low- 
power,  without  a  cover-glass,  and  when  individual  fibrillae  are  visible, 
remove  the  excess  of  carbol-xylol  with  filter  paper  and  mount  in  xylol- 
balsam. 

No.  26. — Ends  of  muscle-fibers. — Place  the  fresh  gastrocnemius 
muscle  of  the  frog  in  20  c.c.  of  concentrated  potash-lye,  and  treat  further 
like  No.  21  a.  With  low  magnification  one  sees  the  ends  of  the  muscle- 
fibers  and  numerous  swollen,  shining  nuclei  (Fig.  56,  3). 


I  I  2  HISTOLOGY. 

No.  27. — Branclied  muscle -fibers.  —  Remove  the  tongue  from  a 
recently  killed  frog  (it  is  attached  in  front  to  the  lower  jaw,  is  free  behind) 
and  place  it  in  20  c.c.  of  pure  nitric  acid,  to  which  about  5  gm.  of  potas- 
sium chlorate  have  been  added  (some  undissolved  chlorate  must  remain 
in  the  bottom  of  the  vessel).  In  a  few  hours,  with  glass  rods,  carefully 
transfer  the  tongueto  30  c.c.  of  distilled  water,  which  must  be  frequently 
changed.  In  this  the  tissue  may  remain  a  week,  though  it  can  be  used 
at  the  end  of  twenty-four  hours.  For  this  purpose  put  it  in  a  test-tube 
half  filled  with  water  and  shake  it  several  minutes  ;  the  tongue  will  fall 
to  pieces.  Turn  the  contents  of  the  test-tube  into  a  capsule  and  in  an 
hour  or  later  place  a  little  of  the  sediment  that  has  been  deposited  in  the 
meanwhile  in  a  drop  of  water  on  a  slide.  The  tissue  may  be  further 
isolated  with  the  teasing  needles,  but  in  most  cases  this  is  superfluous. 
Examine  with  the  low  power.  Stain  under  the  cover-glass  with  picro- 
carmine  (p.  53).      Mount  in  dilute  glycerol  (p.  50).     (Fig.  56,  4.) 


IV.  THE  NERVE  TISSUES. 

The  elements  of  the  nerve  tissues,  in  an  early  embryonal  stage,  are 
without  exception  cells  having  a  spherical  form,  the  so-called  neuroblasts. 
In  the  course  of  development  they  become  pyriform,  the  narrow  end 
grows  out  as  a  long,  thin  process,  often  extending  the  length  of  a  meter, 
and  terminates  in  a  free,  branched  end ;  it  is  named  the  nerve-process. 
From  the  body  of  the  cell,  now  termed  a  nerve-cell,  other  processes  may 
arise,  which,  however,  are  short  and  divide  dichotomously  ;  they  are 
called  dendrites.  Delicate  lateral  branches,  the  collateral  fibers,  may 
grow  from  the  nerve-process.  The  nerve-cell  and  the  nerve-process  to- 
gether form  a  cellular  unit,  the  neuron  (neurodendron).  The  dendrites 
and  collaterals  are  to  be  regarded  as  secondary  processes  of  the  neuron. 

The  nerve-process  may  remain  naked  throughout  its  course,  or  it 
may  receive  different  sheaths  ;  these  are  the  neurilemma,  or  sheath  of 
Schwann,  and  the  medullary  slieath.'^  Both  clothe  the  nerve-process 
only  in  a  portion  of  its  length.  There  are  stretches  in  which  the  nerve- 
process  is  entirely  without  covering,  is  naked  (Fig.  58,  a);  stretches  in 
which  it  is  enveloped  only  by  the  neurilemma  (Fig.  58,  b^  or  only  by  the 
medullary  sheath  (Fig.  58,  <r),  and,  finally,  stretches  in  which  both 
sheaths  are  present  (Fig.  58,  d);  in  this  case  the  medullary  sheath  is 
always  the  innermost  envelope,  lies  directly  upon  the  cylindrical  nerve- 
process,  and  is  itself  ensheathed  by  the  neurilemma.  The  nerve- process 
always  occupies  the   longitudinal  axis  ;   hence  the  name    axis-cylinder. 

*The  neurilemma  is  of  connective  tissue  origin,  the  wji/f/m  forming  the  medullary  sheath 
(p.  121),  according  to  recent  research,  originates  in  the  blood  and  is  conducted  to  the  nerve- 
processes  by  connective-tissue  cells, — in  the  central  nervous  system  by  glia-cells. 


THE     TISSUES. 


113 


Dendrites. 


Owing  to  the  often  great  length  of  the  nerve -process,  it  is  not  possible 
to  investigate  the  neuron  as  a  whole. 
As  a  rule,  it  is  seen  only  in  frag- 
ments, either  the  nerve-cell  or  the 
nerve-process.  This  explains  the 
former  division  of  the  elements  of 
the  nerve  tissues  into  iicrve-cells  2ir\d 
ncrve-fibcrs,  the  latter  being  the 
nerve-processes  with  their  sheaths. 
There  are  no  independent  nerve- 
fibers,  each  so-called  fiber  is  a  pro- 
cess of  a  nerve-cell ;  if  the  connec- 
tion between  the  fiber  and  the  cell 
is  broken,  the  fiber  dies  cellulifu- 
galward  from  the  point  of  solution 
of  continuity.  For  practical  rea- 
sons the  old  classification  of  nerve- 
cells  and  nerve-fibers  is  retained. 


A.    NERVE-CELLS. 

Nerve-cells  (ganglion-cells) 
are  found  in  the  ganglia,  in  the  or- 
gans of  special  sense,  along  the 
course  of  cerebrospinal,  as  well  as 
sympathetic  nerves,  but  principally 
in  the  central  nervous  system.  They 
differ  greatly  in  size  (4  to  135  ^«  and 
more)  and  in  form.  There  are  spheri- 
cal and  spindle-shaped  nerve-cells 
and  irregularly-stellate  forms  are 
very  common  ;  the  latter  are  those 
in  which  the  protoplasm  sends  oft 
several  processes.  Nerve-cells  hav- 
ing two  processes  are  termed  bipolar, 
those  having  several  processes  vml- 
tipolar  ganglion-cells  (Fig.  59). 
There  are  also  ?^;///>^/a;' nerve -cells  ; 
these  occur  in  the  sympathetic  nerve 
of  amphibians  and  universally  in 
the  olfactory  mucous  membrane  (Fig.  348),  They  actually  possess  but 
a  single  process.     The  nerve-cells  of  the   spinal   ganglia,  on  the  other 


Terminal  ramification. 


Fig.  5S.— D1AGR.A.M  OF  A  Neuron. 


114 


HISTOLOGY. 


hand,  are  only  apparently  unipolar  ;  in  developmental  epochs  they  were 
bipolar  and  then  became  unipolar  by  the  gradual  approach  of  the  pro- 
cesses, which  eventually  leave  the  cell  by  a  common  stalk,  from  which 
they  soon  diverge  at  right  or  obtuse  angle.  These  are  the  cells  de- 
scribed as  having  T-shaped  or  Y-shaped  processes.  Apolar  cells,  that 
is,  nerve -cells  without  processes,  are  either  immature  forms  or  artifacts, 
the  processes  having  been  torn  off  in  the  manipulation  required  for 
isolation. 

Each  nerve-cell  consists  of  a  protoplasm  and  of  a  quite  character- 
istic vesicular  nucleus,  poor  in   chromatin  and  enclosing  a  conspicuous 


I.  Bipolar  cells. 


2.  Cell  on  T. 


3.  Spinal  ganglion-cell. 


cell. 


Fig.  59. — Different  Forms  of  Nerve-cells.  X  236.  i.  From  the  spinal  ganglion  of  a  six-day  embrjo 
chick.  2.  From  the  spinal  ganglion  of  a  calf.  Technic  No.  86.  3.  Of  man  ;  the  nerve-process  torn 
off.     Technic  No.  28.     4.  From  the  human  spinal  cord.     Technic  No.  29. 

nucleolus.      In  many  nerve-cells  a  centrosome  has  been  demonstrated. 
A  cell-membrane  is  wantins". 


The  protoplasm  of  nerve-cells  possesses  a  very  complicated  structure.  It 
contains  : 

I.  Fibrils,  which  occur  arranged  in  bundles,  as  well  in  the  body  as  in  the 
processes  of  the  nerve-cell  ;  they  may  enter  from  one  process,  simply  pierce  the 
cell,  divide  and  make  their  exit  in  several  processes  ;  or,  reversed,  they  may 
assemble  from  different  processes  and  pass  out  in  a  single  process,  or  they  may 
form  a  dense  tangle — more  rarely  an  actual  network — in  the  body  of  the  cell. 
These  fibrils  are  to  be  regarded  as  the  conducting  nervous  elements,  but  whether 
they  are  the  only  ones  is  doubtful,  for  it  is  well  known  that  conduction  can  also 
be  effected  without  demonstrable  nerve-fibrils,  simply  by  the  protoplasm. 


THE     TISSUES. 


115 


2.  Delicate  canaliculi,  the  trophospongium  (Fig.  62),  and  the  apparato 
reticulare  (Fig.  63),  see  page  64.  In  the  lower  vertebrates  canaliculi  contain- 
ing blood-cells  have  been  found. 


Fig.  60.— Two  Forms  of  Multipolar  Nerve-cells  from  the  Ventral  Horn  of  the  Spinal  Cord 
OF  a  Newborn  Rabbit,  showing  the  Richly  Branched  Protoplasmic  Processes,  n.  Nerve- 
process.     X  60.     Technic  No.  76.     (Schaper.) 

3.   Granule  groups,  which  consist  partly  of  pigment,  partly  of  substances 
that  can  be  made  visible  only  by  special  methods.     These  substances,  the  Nisst  s 


Nucleus. 


Nissl's. bodies 


Fig.  61. — Ganglion-cell  of 
the  Spinal  Cord  of  a 
Child.  X  430.  Technic 
No.  30. 


Sheath.        Canahculi. 

Fig.  62.— Spinal  Ganglion- 
cell  OF  an  Adult  Cat. 
X  430.     Technic  No.  30. 


Apparato  reticulare. 
Fig.    63.— Spinal    Ganglion- 
cell  OF  a  Newborn  Kit- 
ten.   Copy  after  Golgi. 


bodies  ("  tigroid  "),  that  do  not  belong  to  all  nerve-cells,  are  very  differently 
shaped, "-J^  are  sometimes  spherical,  sometimes  polyhedral  aggregations  of  gran- 

*  This  varied  structure  of  the  protoplasm  makes  it  intelligible  that,  despite  the  numerous 
interlacing  ramifications  of  the  nerve-cells  and  their  processes,  the  excitation  is  not  a  diffuse  but 
an  orderly  one,  running  in  definite  pathways. 


ii6 


HISTOLOGY. 


ules,  sometimes  spindles  and  bands,  and  fill  the  spaces  between  the  strands  of 
fibrils,  the  canaliculi  of  the  trophospongium.  They  occur  also  in  the  dendrites 
(see  below),  but  extremely  seldom  in  the  nerve-process.  The  bodies  of  Nissl 
are  in  so  far  of  especial  significance,  since  in  over-fatigue  and  in  abnormal 
states  of  the  nerve-cell,  also  in  old  age,  they  change,  even  almost  wholly  dis- 
appear. The  circumstance  that  these  changes  are  of  early  occurrence,  appearing 
before  any  functional  disturbance  of  the  conducting  elements  can  be  observed, 
indicates  the  function  of  the  bodies  of  Nissl  to  be  more  nutritive  (perhaps  form- 
ative) than  nervous. 

The  processes  of  nerve-cells  are  of  two  kinds,  most  readily  distin- 


Dendrites 


Cell-body 


Nerve-process. 


Fig.  54. — Nerve-cell  (Cell  of  Purkinje)  from  a  Section  through  the  Human  Cerebellar 
Cortex.    X  180.    Technic  No.  80. 


guished  in   multipolar   nerve-cells  :     i.    One   process,   the   nerve-process 
(axis-cylinder,  axon,   Fig.    64),   the    only  one    of  its  kind  ;*    it    is    the 

*It  is  said  there  are  cells  with  several  nerve-processes  (e.  g. ,  Cajal's  cells  in  the  cerebral 
cortex).  In  bipolar  ganglion-cells,  both  processes  of  %vhich  become  axis-cylinders  of  medul- 
lated  nerve-fibers  (spinal  ganglion-cells  of  lower  vertebrates  and  of  embryos),  the  central  pro- 
cess going  to  the  central  nervous  system  corresponds  to  the  nerve-process,  the  peripheral 
process  to  a  dendrite.  This  conception  is  supported  by  the  observation  that  in  the  bipolar  cells 
of  the  cochlear  nerve  the  peripheral  process  develops  precisely  like  a  dendrite  and  only  later 
assumes  the  character  of  a  nerve-fiber. 


THE     TISSUES. 


117 


first  outgrowth  of  the  embryonal  spherical  nerve-cell  and  is  character- 
ized by  its  hyaline,  smooth-bordered  appearance  ;  it  conducts  from  the 
cell — cellulifugal.  2.  Many  processes,  the  dendrites  (protoplasmic 
processes,  Fig.  64) ;  they  are  a  later  outgrowth  of  the  nerve-cell,  are 
thicker,  granular  or  finely  striated,  and  often  beset  with  varicosities  ;  they 
conduct  toward  the  cell — cellulipetal.  The  dendrites  divide  repeatedly  and 
so  can  form  an  extraordinarily  rich  arborization,  the  finest  twigs  of 
which  terminate  in  free  ends  (Fig.  64) ;  in  this  way  the  cell-body  acquires 
an  enormous  superficial  enlargement,  which,  on  the  one  hand,  exalts  the 
sustentative  power,  on  the  other  hand,  the  susceptibility  to  nerve  stimuli 


Ramification  of  the 
nerve-process. 


Fig.  65. — Two  Nerve-cells.    X  200.    A,  From  a  section  of  the  spinal  cord  of  a  human  embryo  six 
months  old.    B,  From  a  section  of  the  brain  of  a  cat.    Technics  No.  76  and  No.  79. 

— these  latter  being  transmitted  by  adjacent  terminal  ramifications  of  nerve- 
processes. 

According  to  the  behavior  of  the  nerve-processes  two  types  of  gang- 
lion-cells are  distinguished. 

I.  In  cells  of  the  first  type  (Deiters's  type)  the  nerve-process  becomes 
the  axis-cylinder  of  a  medullated  nerve-fiber,  which  after  running  a  long 
course,  often  measuring  many  centimeters,  always  terminates  in  an  ex- 
tremely delicate  ramification  ;  these  cells  are  described  as  nerve-cells  with 
a  long  nerve-process  (Fig.  65). 

During  its  course  such  a  nerve-process  gives  off  a  number  of  delicate, 
branching,  lateral  twigs  ("collaterals,"  "  paraxons  ")  ;    by  no  means  rarely 


Il8  HISTOLOGY. 

there  also  occurs  a  division  of  the  nerve-process  in  two  equal  nerve-processes 
(see  The  Spinal  Cord,  "  plurifunicular  cells,"  p.  192,  remark*). 

2.  In  cells  of  the  second  type  (Golgi's  type)  the  nerve-process,  by  con- 
tinual division,  resolves  in  a  nervous  ramification  in  the  vicinity  of 
the  cell  ;  these  cells  are  called  nerve-cells  with  a  short  nerve-process 
(Fig.  65). 

Whether  the  nerve-processes  belong  to  the  one  or  the  other  type, 
their  terminal  ramifications  are  free,  in  the  respect  that  they  never 
directly  pass  into  the  terminal  ramifications  of  other  nerve-processes  or 
dendrites.  Accordingly  there  is  no  nervous  reticidum  formed  of  the 
processes  of  several  nerve-cells,  but  only  a  dense  felt-work  {neuripilem) 
consisting  of  interlacing  ramifications.  Different,  on  the  other  hand,  is 
the  behavior  of  the  terminal  ramifications  of  an  individual  nerve-process. 
This  may  be  very  diverse  ;  sometimes  there  is  only  a  coarse  arborization 
with  free  endings,  sometimes  the  extremity  of  a  nerve-process  passes 
with  numerous  divisions  into  an  uncommonly  fine,  close  reticulum  * 
("  Golgi-net,"  "  nerve-lattice  "),  that  lies  immediately  upon  the  bodies 
and  dendrites  of  other  nerve-cells.  It  has  not  been  demonstrated  that 
in  a  Golgi-net  of  one  nerve-process  terminal  ramifications  of  other  nerve- 
processes  participate. 

Therefore  each  neuron  is  in  itself  a  closed,  independent  structure,  that 
communicates  with  other  neurons,  not  by  anastomoses  but  only  by  contact, 
not  per  continuitatem  but  per  contiguitatem.f 

B.     NERVE-FIBERS. 

Dependent  upon  the  presence  or  absence  of  the  medullary  sheath, 

*  It  is  probable  that  the  Golgi-net  is  not  formed  of  the  terminal  ramifications  themselves, 
but  consists  of  a  peculiar  substance  in  which  the  fibrils  of  the  ramifications  run ;  the  proof  is 
still  required  that  the  fibrils  form  a  true  net.  Each  nerve-cell  of  the  central  nervous  system 
is  provided  with  a  reticulum  of  Golgi  ;  a  single  nerve-cell  may  be  embraced  by  several  vari- 
ously fashioned  terminal  ramifications  of  different  nerves. 

f  Whether  this  statement  is  invariably  valid  is  doubtful.  In  the  retina  and  in  the  electric 
organ  of  the  torpedo  true  nets  formed  of  processes  of  several  nerve-cells  have  been  described  ; 
von  Thanhofer  demonstrated  to  me  preparations  that  show  distinct,  delicate  anastomoses  be- 
tween cells  of  the  spinal  cord.  Such  a  connection  does  not  affect  the  neuron  theory  any  more 
than  the  intercellular  bridges  do  the  cell  theory.  A  few  authors  describe  the  Golgi-net  as 
"diffuse"  and  thereby  endeavor  to  rehabilitate  the  old,  long-abandoned  hypothesis  that  the 
nerve-fibers  arise  from  a  general  nerve-plexus.  Therewith  the  nerve-cells  are  pushed  aside  as 
secondary  elements,  having  no  significance  in  nervous  functions.  This  view,  which  is  in  glar- 
ing opposition  to  the  neuron  theory,  is  still  lacking  in  sound  anatomic,  as  well  as  experimental, 
evidence.  When  in  the  following  nervous  networks  and  plexuses  are  spoken  of  it  is  to  be  thus 
understood,  that  from  nerve-fiber  bwidles  a  few  nerve-fibers  branch  off  to  join  other  bundles.  In 
this  transfer  of  fibers  a  direct  transition  of  one  nerve-fiber  into  another,  as  a  rule,  does  not 
occur. 


THE    TISSUES. 


119 


nerve-fibers  are  divided  into  mcdidlated  and  nonincdidlated.  Each  divi- 
sion is  susceptible  of  a  subdivision  dependent  on  the  presence  or  absence 
of  the  neurilemma. 


I.   Nonmedullated  Nerve-fibers. 

[a)    Without  a  NeurUevi^na. 

These  fibers  consist  of  the  axis-cylinder  (nerve-process)  alone  ;  they 
are  therefore  described  as  "  naked  "  and  are  found  in  the  olfactory  nerve, 
where,  grouped  in  bundles,  they  are  held  together  by  connective  tissue. 
Similar  are  many  fibers  of  the  sympathetic  nerve,  the  so-called  Reniak's 
fibers,  which  are  transparent,  cylindrical  or  bandlike  in  form,  from  3  to 
7  ix  wide,  about  2  a  thick,  and  exhibit 
faint  longitudinal  striation  ;  they  likewise 
consist  of  bundles  of  naked  axis-cylin- 
ders *  and  a  very  delicate  sheath,  on 
which  here  and  there  lie  flat  connective- 
tissue  cells  with  oblong  nuclei.  The 
sheath  is  said  to  correspond  to  the  endo- 
neurium  or,  according  to  some  authors, 
to  the  neurilemma.  (See  the  chapter  on 
the  Central  Nervous  System.) 

While  the  fibers  so  far  described 
exhibit  the  same  structure  throughout 
their  length,  there  are  nerve-fibers  of 
which  only  certain  divisions  are  naked 
axis-cylinders.  Such  divisions  occur  as 
peripheral  endings  of  the  nerves  of  spe- 
cial sense  and  of  sensory  as  well  as 
motor  nerves  ;  also  the  first  division  of 
the  nerve-process  proceeding  from  the  nerve-cell  is  a  naked  axis-cylin- 
der (./.  Fig.  58). 

{p)    With  a  Neurilemma. 
Fibers  consisting  in  their  entire  length   of  an    axis-cylinder   and  a 
neurilemma  are  found  in  many  invertebrates  and  in   cyclostoma.     They 
occur  as  divisions  in  the  course  of  the  cerebrospinal  nerve-fibers  (Fig. 
58,-^). 


Fig.  66. — Teased  Preparation  of  the 
Sympathetic  Nerve  of  a  Rabbit. 
I.  Nonmedullated,  2,  thin  medullated 
nerve-fibers  ;  3,  ganglion-cell ;  the  large 
nucleus  has  lost  its  characteristic  ap- 
pearance in  consequence  of  the  treat- 
ment with  osmic  acid  ;  4,  nuclei  of  con- 
nective-tissue capsule;  5,  fine  connec- 
tive-tissue fibers.  X  240.  Technic  No. 
36. 


*  By  Remak's  fibers  some  authors  understand,  not   bundles  of  naked  axis-cylinders,  but 
individual  axis-cylinder  processes  of  sympathetic  ganglion-cells. 


I20 


HISTOLOGY. 


2.   Medullated  Nerve-fibers. 

(a)    Without  a  Nenrileimna. 
Among  these  are  no  fibers  that  possess  the  medullary  sheath  in  their 
entire  length  ;  this  always  clothes  only  one  division  of  the  axis-cylinder. 
Fibers  consisting  of  axis-cylinder  and  medullary  sheath  alone  (Fig.  58,  r) 
occur  only  in  the  central  nervous  system. 

(^)    With  a  Neurilemma. 
Medullated  fibers  possessing  a  neurilemma  are  found  in  the  trunks 
and  branches  of  the  cerebrospinal  nerves,  also  in  the  sympathetic  nerve, 
and  vary  in  thickness  from  i  to  20  ;/. 

Axis-  Medullary        Axis-  Nucleus  of 

cylinder.        sheath.        cylinder.        neurilemma. 


Fig.  67. — Medullated  Nerve-fibers  from  the  Sciatic  Nerve  of  a  Frog.  X  280.  i,  Normal,  2, 
shrunken,  3,  twisted  axis-cylinder ;  4,  node  of  Ranvier  ;  5,  neurilemma  with  nucleus.  Technic  No.  33. 
6,  7,  8,  and  9.  Fresh  medullated  nerve-fibers;  10,  post-mortem  distortion  of  medullary  substance  ;  r, 
annular  constriction  ;  /,  notches  of  Lanterman  ;  i,  cylindro-conical  segment.     Technic  No.  31  a. 

The  thickness  of  the  nerve-fiber  bears  no  relation  to  its  motor  or 
sensory  nature,  but  appears  to  be  determined  by  its  length  :  the  longer 
its  course  the  thicker  is  the  fiber.  Division  of  the  medullated  fibers 
occurs  (i)  throughout  the  central  nervous  system,  principally  where  the 
collateral  fibers  diverge  at  right  angles  into  the  white  substance,  and  (2) 
in  the  peripheral  nervous  system  shortly  before  their  ultimate  distribu- 
tion (Fig.  58). 

The  medullated  nerve-fibers  have  a  brief  lease  of  life.  They  de- 
generate by  a  gradual  breaking  down  of  the  medullary  substance  and 
axis-cylinder  into  a  granular  mass  containing  numerous  nuclei;  in  this 


THE     TISSUES. 


121 


mass  both  parts  are   regenerated,    the   axis-cyhnder   probably   by   out- 
growth of  the  nerve-process  of  the  nerve-cell. 

Regarding  their  finer  structure  and  peculiar  properties,  the  three  con- 
stituent parts  of  nerve-fibers  comport  themselves  in  the  following  manner  : 

1.  The  axis-cylinder,  the  most  essential  part  of  every  nerve-fiber, 
exhibits  a  delicate  longitudinal  striation,  which  is  the  optical  expression 
of  its  fibrillar  structure.  Each  fibrilla  represents  a  special  conducting 
path  and  is  cemented  to  neighboring  fibrillje  by  a  small  amount  of  highly 
aqueous,  finely  granular  or  homogeneous  interstitial  substance,  the  neuro- 
plasui  (axoplasm). 

2.  The  medullary  sheath  consists  of  a  semi-fluid,  highly  refracting, 
fatty  substance,  the  myelin,  which  imparts  to  fresh  medullated  fibers  the 
appearance  of  entirely  homogeneous,  glistening, 

opaque    cylindrical    threads,   the    structure    of  ,     j 

which  can  only  be  perceived  by  the  help  of 
reagents.  Often  it  is  seen  that  the  medullary 
sheath  is  not  continuous,  but  is  divided  at 
slightly  irregular  intervals  by  oblique  incisions, 
the  Lanterman' s  notches,  into  the  "  cylindro- 
conical  "  segments,  which  seem  to  be  united  to 
each  other  by  cement-substance  *  (Fig.  67,  9). 
On  treatment  with  various  reagents  the  totally 
homogeneous  myelin  of  living  nerve-fibers 
undergoes  partial  transformation  as  it  dies  ;  at 
first  the  nerve-fiber  exhibits  a  double  contour,t 
later  the  myelin  rolls  up  into  peculiar  spher- 
ical masses  (Fig.  67,  10). 

At  certain  places  marked  by  ring-like  con- 
strictions the  medullary  sheath  is  wanting,  so 
that  the  axis-cylinder  and  the  neurilemma  come 
into  contact.  These  annular  constrictions  are  termed  nodes  of  Ranvier 
(Fig.  6j,  r) ;  they  are  the  localities  where  the  nutritive  fluid  can 
approach  the  axis-cylinder.  In  the  vicinity  of  the  nodes  the  axis- 
cylinder  is  often  provided  with  a  biconical  enlargement  (Fig.  69), 
due  to  a  local  accumulation  of  neuroplasm.      The  treatment  with  silver 


Fig. 


Medullated  Nerve- 
fibers  OF  A  Frog, treated 
WITH  Silver  Nitrate  Solu- 
tion. X  560.  I.  At  r,  node 
of  Ranvier  ;  a,  axis-cylinder, 
of  which  only  a  small  extent 
is  silvered  ;  6,  biconical  swell- 
ing displaced  downward 
owing  to  manipulation.  2. 
Axis-cylinder  with  the  sil- 
vered portion  in  situ,  at  a. 
3.  Axis-cylinder  with  cross- 
markings.  The  myelin  is  not 
visibleby  this  method.  Tech- 
nic  No.  35. 


*  Many  authors  regard  these  notches  as  artifacts;  they  appear  very  quickly,  even  in 
fibers  just  removed  from  the  animal. 

"f  Thence  the  old  designation  :  "  double-contoured  or  dark-bordered  nerve-fiber."  How- 
ever it  is  questionable  whether  the  double  contour  lines  are  a  coagulation  product,  for  they 
have  been  seen  also  in  the  living  animal.  In  this  case  the  two  contours  would  correspond  to 
the  outer  and  inner  boundaries  of  the  sheath. 


122  HISTOLOGY. 

nitrate  solution  reveals  the  neuroplasm  at  the  nodes  (Fig.  68,  r),  as  well 
as  a  very  distinct  transverse  marking  on  the  adjacent  portions  of  the 
axis-cylinder.*  Each  peripheral  medullated  nerve-fiber  is  provided  with 
nodes,  at  intervals  of  from  0.08  mm.  in  thin  to  i  mm.  in  thick  fibers, 
dividing  it  into  "  interannular  "  segments. 

3.  The  iieiirilemma,  or  sheath  of  Schwann,  is  a  delicate,  structure- 
less membrane,  against  the  inner  surface  of  which  lie  elliptical  nuclei' 
surrounded  by  a  minimal  amount  of  protoplasm  (Fig.  67,  5). 

The  union  of  the  two  elements  of  the  nerve  tissues  in  the  peripheral 
nervous  system  is  secured  by  means  of  connective  tissue,  which  contains 
the  ramifications  of  the  blood-vessels  ;  in  the  central  nervous  system 
they  are  united,  not  only  by  connective  tissue,  but  by  the  netiroglia 
(p.  201). 

TECHNIC. 

No.  28. — Ganglion-cells,  fresh. — Tease  a  small  piece  of  the  Gas- 
serian  ganglion  in  a  drop  of  salt  solution  and  stain  under  the  cover-glass 
with  picrocarmine  for  two  minutes  (p.  53).  The  processes  of  the  cells 
usually  tear  off  (Fig.  59,  3). 

The  nerve-cells  of  the  cerebral  and  the  cerebellar  cortex  may  be 
prepared  in  the  same  way  ;  the  processes  likewise  are  easily  lost. 

No.  29. — Multipolaj"  ganglion-cells  of  the  spinal  cord. — Remove  with 
the  scissors  as  well  as  possible  the  white  substance  of  a  fresh  spinal  cord 
and  place  the  gray  residue,  divided  into  pieces  from  i  to  2  cm.  long,  in 
highly  diluted  chromic  acid  solution  (5  c.c.  of  the  0.05  per  cent,  solution, 
page  21,  to  45  c.c.  of  distilled  water).  After  from  i^  hours  to  8  days 
(the  time  varies  according  to  the  outside  temperature)  the  spinal  cord  is 
macerated  to  a  soft  mass,  that  is  to  be  carefully  transferred  into  20  c.c. 
of  undiluted  neutral  carmine  solution  (p.  24).  The  pieces  remain  in  the 
stain  for  from  10  to  20  hours,  then  are  placed  in  50  c.c.  of  distilled  water, 
in  order  to  wash  out  some  of  the  color,  and  after  5  minutes  the  tissue  is 
ready  to  spread  in  a  thin  film  on  a  dry  slide.  With  a  little  practice  the 
ganglion-cells  can  be  distinguished  by  their  brilliantly  stained  red  nuclei ; 
of  the  bodies  and  processes  nothing  is  visible  to  the  unaided  eye.  Let 
the  film  dry  thoroughly  and  then  cover  it  over  with  a  cover-glass  on  the 
under  side  of  which  a  drop  of  xylol-balsam  is  suspended  (Fig.  59,  4). 

No.  30. — NissV s  bodies. — For  the  exhibition  of  Nissl's  bodies  fix  and 
harden  in  absolute  alcohol  (p.  31)  a  piece  i  cm.  long  of  the  spinal  cord 
freed  from  the  pia  (the  lumbar  enlargement  is  best,  owing  to  its  large 
cells)  and  embed  it  in  paraffin  (see  Microtome  Technic).  Microtome  sec- 
tions are  placed  in  5  c.c.  of  xylol,  then  transferred  to  an  equal  quantity 
of  absolute  alcohol  and  after  a  minute  to  70  per  cent,  alcohol.  From 
this  the  sections  are  put  into  5  c.c.  of  a  2  per  cent,  aqueous  solution  of 

*  These  strise  are  artifacts;   for  their  significance,  see  p.  45,  remarlc*. 


THE     TISSUES.  .  1 23 

fuchsia,  that  is  heated  over  a  flame  until  bubbles  rise.  Then  the  some- 
what crinkled  sections  are  lifted  with  a  needle  into  a  capsule  containing 
a  mixture  of  9  c.c.  of  absolute  alcohol  and  i  c.c.  of  anilin  oil,  in  which 
the  decolorization  occurs.  In  about  10  minutes  renew  the  alcohol-anilin 
mixture.  After  5  minutes  transfer  the  sections  to  absolute  alcohol  and 
after  i  minute  to  xylol.  Mount  in  xylol-balsam.  The  preparations  keep 
for  a  long  time.      (Fig.  61.) 

The  canalicuU  of  the  ganglion-cells  can  be  shown  by  fixing  in  sublimate- 
picric  acid  (equal  parts  of  No.  20,  p.  22,  and  No.  26,  p.  22).  Further  treat- 
ment as  with  Zenker's  fluid  (p.  32).  Stain  thiti  microtome  sections  with 
Heidenhain's  iron-hematoxylin  (p.  44)  and  examine  with  an  immersion  lens. 

No.  31. — Fi'csJl  medullatcd  nerve-fibers. — Expose  the  sciatic  nerve 
of  a  frog  just  killed.  With  delicate  scissors  cut  it  at  the  level  of  the 
popliteal  space  and  about  i  cm.  higher.      Isolate  in  a  drop  of  salt  solution. 

No.  31  a. — Better  still,  tease  on  a  dry  slide  by  the  "half-drying" 
method.  Hold  the  lower  end  of  the  nerve  with  one  needle,  with  another 
needle  separate  the  nerve  bundles  along  half  the  length  of  the  nerve  ; 
a  thin  shining  membrane  will  span  the  interval  between  the  separated 
bundles.  Add  a  drop  of  salt  solution  and  apply  a  cover-glass.  The 
membrane  contains  numerous  isolated  nerve-fibers.  The  manipulation 
must  be  done  very  rapidly  (in  about  fifteen  seconds),  so  that  the  nerve- 
fibers  do  not  become  dry  (Fig.  (ij ,  6,  7,  8,  9). 

No.  32. — Alterations  of  the  viedullary  sheath. — Treat  No.  31  a  with 
water,  place  a  drop  at  the  edge  of  the  cover-glass  and  let  it  flow  under. 
In  a  few  minutes  the  formation  of  the  myelin  drops  begins  (Fig.  67,  10). 

No.  33. — The  axis-cylinder. — Tease  dry  (like  No.  31  a)  and  stain 
with  methylene  blue  (p.  42)  ;  the  nodes  of  Ranvier  stain  first,  and  often 
so  deeply  that  the  axis-cylinder  cannot  be  distinguished  there  (Fig.  6^,  4). 
Frequently  the  axis-cylinder  shrinks  and  becomes  displaced  within  the 
medullary  sheath,  or  it  becomes  convoluted  (Fig.  6'/,  2,  3).  On  the  ad- 
dition of  glycerol  the  medullary  substance  can  no  longer  be  distinctly 
recognized,  but  the  nuclei  of  the  neurilemma  are  often  rendered  plainly 
visible  (Fig.  6^,  5).  If  it  is  desired  to  preserve  in  xylol-balsam  drain  off 
the  solution  of  ammonium  picrate  after  about  18  hours,  cautiously 
rinse  with  water,  and  let  the  preparation  dry  in  the  dark.  Then  mount 
straightway  in  balsam. 

No.  34. — Exhibition  of  the  axis-cylinder  zvitli  chromic  acid. — Expose 
the  sciatic  nerve  of  a  rabbit  recently  killed,  being  careful  not  to  touch  it ; 
place  a  match-stick  parallel  to  the  long  axis  of  the  nerve  and  secure  it 
by  means  of  ligatures  at  the  upper  and  lower  ends  ;  cut  the  nerve  on  the 
farther  side  of  each  ligature  and  place  it,  with  the  wood,  in  100  c.c.  of  a 
0.1  per  cent,  chromic-acid  solution  (p.  21). 

In  about  twenty-four  hours  cut  the  ligatures  and  tease  a  piece  of  the 
nerve,  from  0.5  to    i    cm.   long,    separating  it  into  bundles,    not  fibers. 


124 


HISTOLOGY, 


Put  the  bundles  back  into  the  chromic-acid  solution  ;  after  twenty-four 
hours  transfer  them  to  50  c.c.  of  distilled  water,  and  after  two  or  three 
hours  to  30  c.c.  of  gradually  strengthened  alcohols  to  harden  (p.  35). 
It  is  advantageous  to  leave  the  bundles  for  a  long  time,  one  to  eight 

weeks,  in  90  per  cent,  alcohol,  as 
they  are  then  more  readily  stained. 
After  the  hardening  the  bundles 
are  to  be  teased  in  a  drop  of  pic- 
rocarmine,  placed  in  the  moist 
chamber,  and  after  the  staining  is 
completed  (which  according  to 
the  length  of  time  the  tissue  was 
allowed  to  harden  in  the  alcohol 
requires  from  one-half  to  three 
days),  preserved  in  acidulated  gly- 
cerol (p.  53).  The  nodes  of  Ran- 
vier  are  not  so  distinct  as  in  fresh 
and  in  osmium  preparations,  but 
appear  as  delicate  transverse  lines  (Fig.  69).  The  somewhat  shrunken 
axis-cylinder  and  the  nuclei  are  stained  a  fine  red.*  Not  seldom  the 
axis-cylinder  is  displaced,  so  that  the  biconical  swelling  is  not  at  the 
node,  but  above  or  below  it. 


Node  of  Ranvier 
Biconical  enlargement 


Axis-cylinder. 


Medullary  sheath. 


Nenrilemma. 


Fig.  69.— Nerve-fiber  of  a  Rabbit.    X  560. 


-No-  35- — Nodes  of  Ranvier  and  axis-cylinders. — Preliminary:  Add 
10  c.c.  of  a  I  per  cent,  solution  of  silver  nitrate  to  20  c.c.  of  distilled 
water.  Kill  a  frog,  open  the  abdomen  by  a  crucial  incision,  turn  out  the 
viscera,  and  expose  the  nerves  descending  on  each  side  of  the  vertebral 
column.  Wash  out  the  abdominal  cavity  with  distilled  water  and  pour 
over  the  nerves  about  one-third  of  the  silver  solution.  After  two 
minutes  carefully  cut  out  the  delicate  nerves,  put  them  for  a  half-hour  in 
the  remainder  of  the  silver  solution,  and  place  them  ifi  the  dark.  Then 
transfer  them  to  lO  c.c.  of  distilled  water,  in  which  they  may  remain  for 
from  one  to  twenty-four  hours.  If  a  nerve  is  now  examined  in  a  drop 
of  water,  with  the  low  power,  the  delicate  sheaths  composed  of  flat  cells 
(see  the  cerebrospinal  nerves)  and  numerous  pigment  cells  will  be  seen  ; 
frequently  a  blood-vessel  lies  along  the  nerve.  Now  tease  the  nerve, 
cover  it  and  place  a  small  drop  of  dilute  glycerol  at  the  edge  of  the 
cover-glass.  On  examination  with  the  high  power  little  will  be  seen  of 
the  nodes  and  axis-cylinder,  but  if  the  preparation  be  exposed  for  several 
hours  to  dayhght  (or  a  few  minutes  to  sunlight)  the  reaction  takes  place 
and  the  parts  become  silvered.  The  biconical  swelling  on  the  axis- 
cylinder  often  becomes  displaced  in  teasing  and  is  not  always  readily 
found  by  the  beginner.  With  a  little  practice  pictures  like  that  shown 
in  Fig.  68  are  easily  obtained. 


*  The  intensity  of  the  color  depends  on  the  quality  of  the  picrocarmine,  which  unfor- 
tunately varies  greatly;  it  can  be  improved  by  placing  the  glass  containing  the  teased  bundles 
and  the  stain  on  the  embedding  oven. 


THE     TISSUES.  125 

No.  36. — NonmediiUatcd  nerve-fibers. — Tease  a  portion  of  the 
pneumogastric  nerve  of  a  rabbit  on  a  dry  slide  (No.  31  a),  and  add  a 
few  drops  of  a  0.5  per  cent,  osmic  acid  solution  ;  in  five  or  ten  minutes 
the  medullated  nerve-fibers  become  blackened  (which  may  be  ascertained 
by  examination  with  the  low  power).  Remove  the  osmic-acid  solution 
and  add  a  few  drops  of  distilled  w^ater,  which  should  be  renewed  in  five 
minutes.  In  five  minutes  more  remove  the  water,  add  a  few  drops  of 
picrocarmine,  apply  a  cover-glass,  and  place  in  the  moist  chamber  for 
from  twenty-four  to  forty-eight  hours  ;  then  displace  the  picrocarmine 
with  acidulated  glycerol  (p.  53).  The  tissue  may  be  teased  again  after 
the  staining  is  completed,  which  is  now  more  easily  done  because  the  ele- 
ments are  more  distinctly  seen.  With  high  magnification  the  medullated 
nerve-fibers  appear  blue-black,  the  nonmedullated  pale  gray  and  finely 
striated  longitudinally.  The  sympathetic  nerve  treated  in  the  same  way 
exhibits  more  numerous  nonmedullated  nerve-fibers.  But  this  nerve  is 
somewhat  more  difficult  to  find.  Cut  through  the  greater  cornu  of  the 
hyoid  bone,  through  the  hypoglossal  nerve,  and  push  them  aside  ;  behind 
the  pneumogastric  nerve  lies  the  sympathetic,  which  is  recognized  by  its 
three  or  four  mm.  in  size,  ellipsoidal,  yellowish,  transparent  superior 
cervical  ganglion.  If  the  piece  of  the  nerve  lying  close  under  the  gang- 
lion be  teased,  ganglion-cells  the  majority  of  which  contain  tw^o  nuclei  * 
will  be  obtained  (Fig.  66) ;  it  is  difficult  to  isolate  the  cells  so  that  their 
processes  can  be  distinctly  seen. 


*  Accidentally  in  figure  66  only  the  less  usual  uninucleated  ganglion-cell  is  represented. 


II.    MICROSCOPIC  ANATOMY   OF  THE   ORGANS. 

I.  ORGANS  OF  THE  CIRCULATORY  SYSTEM. 

I.    The    Blood-vessel   System. 

The  blood-vessels  are  composed  of  connective  tissue,  elastic  fibers, 
and  smooth  muscle-fibers,  which,  mingled  in  very  different  relations,  are 
arranged  in  strata.  In  general,  a  uniform  disposition  of  the  elements 
prevails  in  each  stratum  ;  longitudinal  in  the  inner  and  the  outer,  circular 
in  the  middle  stratum.  An  exception  to  this  occurs  in  the  complicated 
structure  of  the  heart  and  in  the  simple  structure  of  the  capillaries. 

THE     HEART. 

The  wall  of  the  heart  consists  of  three  membranes  :  (i)  the  endo- 
cardium ;  (2)  the  powerfully  developed  muscular  layer,  the  myocardium  ; 
(3)  the  epicardium  (visceral  layer  of  the  pericardium). 

(i)  The  endocardhtm  is  a  connective-tissue  membrane,  which  con- 
tains smooth  muscle-fibers  and  numerous  elastic  fibers.  The  latter  are 
less  well  developed  in  the  ventricles  than  in  the  auricles,  where  they 
form  close-meshed  networks  or  are  blended  in  fenestrated  membranes 
(Fig.  36).  The  free  surface,  directed  toward  the  cavity  of  the  heart,  is 
clothed  with  a  simple  layer  of  irregularly  polygonal  epithelial  (endothe- 
lial) cells. 

(2)  The  myocardium  consists  of  a  long-meshed  network  of  muscle- 
fibers  (for  their  structure  see  p.  105)  which  are  enveloped  in  a  delicate 
perimysium  ;  the  course  of  the  strands  of  muscle  is  very  intricate.  The 
musculature  of  the  auricles  is  entirely  separate  from  that  of  the  ventri- 
cles. In  the  auricles  an  outer  transverse  layer  common  to  both  and  an 
inner  longitudinal  layer  independent  in  each  (more  particularly  in  the 
pectinate  muscle  of  the  right  auricle)  can  be  distinguished.  In  addition 
numerous  small  bundles  pursue  independent  courses  in  other  directions. 
The  musculature  of  the  ventricles  is  much  more  irregular  ;  the  bundles 
extend  in  every  direction,  often  describing  a  figure-of-eight  in  their 
course. 

Within  the  territory  of  the  auricles  *  the  perimysium  contains  many 

*  The  muscle  membrane  of  the  auricular  appendages,  on  the  other  hand,  is  poor  in  elastic 
fibers. 

126 


THE    CIRCULATORY    SYSTEM. 


127 


elastic  fibers,  which  multiply  in  old  age  and  which  are  connected  with 
those  of  the  endocardium  and  the  epicardium  ;  within  the  territory  of 
the  ventricles  the  perimysium  contains  no  elastic  elements,  except  those 
belonging  to  the  adv^entitia  of  the  myocardial  blood-vessels.  Between 
the  auricles  and  ventricles  lie  firm  tendon  bands  intermingled  with  elastic 
fibers,  the  aiuutli  fibrosi,  of  which  the  right  is  stronger  than  the  left. 
Similar  but  less  developed  tendons  lie  at  the  arterial  orifices  of  the  ven- 
tricles. Numerous  ends  of  muscle-fibers  or  of  the  muscle  net  are 
inserted  in  these  tendons. 

Lateral  union. 


N. 


:  Blood 
^■^     capillaries. 


V 

Epithelium.  Elastic  Nucleus    Trans-     Nucleus 
fibers,    of  a  con-     verse         of  a 

nective-    sections    muscle- 
tissue    of  muscle-    fiber, 
cell.  fibers. 

Fig.  70.— Fro.m  a  Transverse  Section 


Nuclei  of  connec- 
tive-tissue cells. 


Nucleus 
of  a 

muscle- 
fiber. 


Nucleus 
of  a 
connective- 
tissue  cell. 


Transverse  line. 


Fig.  71. — From  a  Longitudinal  Section 


OF  A  Papillary  Muscle  of  the  Human  Heart,    x  360.    Technic  No.  37. 

(3)  The  epicardium  is  a  connective-tissue  membrane  penetrated  by 
elastic  fibers  and  fat-cells,  which  on  the  outer  surface  is  covered  with  a 
.single  stratum  of  squamous  epithelium.  The  elastic  fibers  of  the 
auricular  epicardium  pass  over  into  the  adventitia  of  the  large  veins  ; 
those  of  the  ventricular  epicardium  are  lost  in  the  conus  arteriosus  and 
do  riot  continue  over  into  the  aorta  and  the  pulmonary  artery. 

The  valves  of  the  heart  are  composed  of  fibrous  connective  tissue, 
which  is  connected  with  that  of  the  annuli  fibrosi,  and  their  surfaces  are 
clothed  by  the  endocardium.      They  contain  muscle-fibers,  but  only  in 


128  HISTOLOGY. 

the  attached  margin,  and  elastic  fibers,  which  are  especially  abundant  in 
the  nodules  of  the  free  edges  of  the  semilunar  valves. 

In  many  mammals  (seldom  in  man,  very  fine  in  sheep)  Furkinje' s  fibers  are 
found  in  the  heart  wall,  usually  close  under  the  endocardium  ;  they  are  strings 
of  clear  cells.  Their  border  layers  contain  cross-striped  fibrillce  extending 
continuously  through  from  cell  to  cell.  Their  nuclei  multiply  partly  by  mito- 
sis, partly  by  amitosis  ;  in  the  latter  case  cell  division  does  not  occur.  These 
cells  must  be  regarded  as  developmental  forms  of  true  cardiac  muscle-fibers, 
since  they  gradually  are  transformed  into  such. 

The  numerous  blood-vessels  of  the  heart  run  in  the  musculature 
according  to  the  typical  arrangement  for  muscles  (see  Organs  of  the 
Muscular  System).  The  epicardium  and  endocardium,  the  latter  only  in 
its  deeper  strata,  also  possess  blood-vessels.  The  semilunar  valves  con- 
tain no  blood-vessels,  the  cuspid  valves  have  them  only  at  their  base,  so 
far  as  their  musculature  extends. 

The  lymph-vessels  dind  the  juice-canals  (see  p.  lOo)  occur  in  colossal 
number  in  the  heart ;  the  latter  form  a  comprehensive  system  embracing 
all  the  free  spaces  between  the  muscle  bundles  and  the  blood-vessels. 

The  many  nerves,  partly  medullated  and  partly  nonmedullated,  aris- 
ing from  the  vagus  and  the  sympathetic,  form  networks  enclosing  numer- 
ous ganglion-cells  ;  the  branches  springing  from  these  networks  are 
partly  motor  (on  every  muscle-fiber  a  nerve-fiber  terminates  in  a  small 
eminence)  and  partly  sensory  ;  the  latter  end  in  terminal  plexuses  of 
different  size,  that  spread  out  over  a  granular  plate  furnished  with  stisl- 
late  (connective-tissue  ?)  cells.  All  the  terminal  plexuses  appear  to  be 
derived  from  medullated  nerves  and  occur  in  great  number,  as  well  in 
the  epicardium  as  in  the  endocardium. 

The  pericardium  consists  of  compact  connective  tissue  intermingled 
with  elastic  fibers,  which  on  its  inner  surface,  that  directed  toward  the 
heart,  is  clothed  with  a  simple  layer  of  squamous  epithelium, 

THE    ARTERIES. 

The  walls  of  the  arteries  consist  of  three  coats  :  i,  the  tunica  intima  ; 
2,  the  tunica  media  ;  3,  the  tunica  externa  (adventitia).  The  elements  of 
the  tunica  media  are  transversely  disposed,  those  of  the  two  other'tunics 
chiefly  longitudinally.  The  structure  and  thickness  of  these  coats  vary 
with  the  size  of  the  artery.  This  makes  their  classification  as  small, 
medium,  and  large  arteries  desirable. 

The  small_art£zies  are  the  precapillary  arteries,  the  arterial  vessels 
shortly  before  their  transition  into  capillaries.  The  intima  consists  of 
elongated,  spindle-shaped  epithelial  cells  and  a  structureless  elastic  mem- 


THE    CIRCULATORY    SYSTEM, 


129 


brane,  the  so-called  internal  elastic  nienibranc  (elastica  interna),  that  in 
somewhat  larger  arteries  assumes  the  character  of  a  fenestrated  mem- 
brane. The  media  is  formed  of  a  single  layer  (in  somewhat  larger  arte- 
ries of  several  layers)  of  circularly  disposed  smooth  muscle -fibers.     The 


Fig.  72. — Small  Arteries  of  Man.  j,  Nuclei  of  intima,  the  outlines  of  the  cells  are  invisible;  m,  nuclei 
of  circularly  disposed  muscle-fibers  of  media  ;  a,  nuclei  of  externa.  A,  artery  with  the  surface  in  focus. 
S,  artery  with  the  lumen  in  focus  ;  at  tn'  the  nuclei  of  the  muscle-fibers  of  the  media  are  seen  in  optical 
cross-section.  C,  small  artery  shortly  before  transition  into  capillaries;  the  media  consists  of  a  few 
isolated  muscle-fibers.     X  240.     Technic  No.  39. 


externa  is  composed  of  fine-fibered,  longitudinally  disposed  bundles  of 
connective  tissue  and  delicate  elastic  fibers.  It  blends  insensibly  with 
the  connective  tissue  supporting  the  arteries. 


Epithelial  cells. 


Boundary  lines  of  smooth  muscle-fibers. 


Fig.  ys.-fEpirHELiuM  of  the  Mesenteric  Artery  of  a  Rabbit,    Surface  view.    X  260.    Technic 

No.  40. 


The  arteries  of  mcdiinn  j-/.crr  comprise  all  the  (remaining)  arteries  of 
the  body  with  the  exception  of  the  aorta  and  the  pulmonary  artery.  The 
intima  of  these  vessels  has  increased  in  thickness  owing  to  the  interposition 
between  the  epithelial  cells  and  the  internal  elastic  membrane  of  net- 
works of  delicate  elastic  fibers  and  a  striped  connective  substance  enclos- 
9 


I30 


HISTOLOGY. 


ing  flattened  cells.*  The  media  no  longer  consists  only  of  circularly 
disposed  smooth  muscle-fibers, f  that  here  are  arranged  in  several  super- 
posed layers,  but  also  contains  wide-meshed  nets  of  elastic  fibers.  The 
proportion  of  the  two  tissues  in  the  individual  arteries  differs  widely  :  in 
the  celiac,  femoral,  and  radial  arteries  the  muscle  tissue  preponderates  ; 
in  the  carotid,  axillary,  and  common  iliac  the  elastic  tissue  is  in  excess. 
The  externa  has  likewise  become  stouter.  Thick  elastic  fibers  occur  in 
especial  profusion  at  the  boundary  of  the   media  and  in  many  arteries 


Epithelium. 

Internal 

elastic 

membrane. 


Intima. 


Media. 


Vasa 

vasorum 


Fig.  74. — Portion  of  a  Cross-section  of  the  Brachial  Artery  of  Man.     X  100.    Technic  No.  37. 


form  an  independent  layer  that  has  been  designated  the  external  elastic 
membrane  %    (Fig.    74).      New   elements   in   the   externa   of    arteries    of 

*  This  subepithelial  layer  is  absent  in  the  larger  branches  of  the  abdominal  aorta,  in  the 
external  iliac,  and  in  the  uterine  arteries  of  young  individuals  ;  in  the  larger  arteries  of  the  brain 
the  internal  elastic  membrane  is  about  three  times  as  thick  as  in  other  arteries  of  like  size  and 
is  characterized  by  longitudinal  bars. 

f  At  the  inner  boundary  of  the  media  longitudinally  disposed  muscle-fibers  occur;  they 
are  especially  well-developed  in  the  subclavian  artery. 

\  In  the  arteries  of  the  brain  the  longitudinally  disposed  elastic  fibers  of  the  externa  are 
very  slightly  developed;  on  the  other  hand,  the  internal  elastic  membrane  is  very  well  devel- 
oped. 


THE    CIRCULATORY    SYSTEM. 


131 


medium  size  are  smooth  muscle-fibers,  that  are  arranged  in  single,  longi- 
tudinally disposed  bundles,  never  in  a  continuous  layer. 

In  the  large  arteries  (aorta  and  pulmonary  artery)  the  epithelial 
cells  of  the  iiitiiiia  are  shorter  and  more  polyhedral  in  outline  than  in 
medium-sized  vessels  ;  immediately  beneath  are  the  subepithelial  layers,  of 
striped  connective  substance,  that  occur  in  the  larger  medium  arteries 
and  that  here  also  enclose  flattened,  stellate,  or  spherical  cells,  as  well  as 
elastic  fiber-nets.      These  fiber-nets  are  the  thicker  the  nearer  they  lie  to 

Epithelium.    -^     -„.     _        .   -     _ --rr-         -* 


Striped  connective  sub- 
stance. 


?undles  of  smooth 
muscle-fibers. 


/ii--: 


Elastic  fibers.    '—=-—- 


~~.^'^"^    1     2 


Elastic  fibers. 


Connective-tissue 
bundles. 


\ 


Fig.  75.— From  a  Cross-section  of  the  Thor.^cic  Aorta  of  Man.     X  100.    Technic  No.  37. 

the  tunica  media  and  finally  pass  into  a  fenestrated  membrane,  which  cor- 
responds to  the  internal  elastic  membrane  of  small  and  medium-size 
arteries.  The  media  of  large  arteries  is  characterized  by  the  preponder- 
ance of  richly  developed  elastic  tissue  over  the  muscular  elements.  In- 
stead of  thin  fiber  networks  close  networks  of  thick  elastic  fibers  or 
fenestrated  membranes  *  occur,  which   regularlv  alternate  with  strata  of 


*  The  elastic  membranes  are  already  present  in  the  larger  middle-sized  arteries  ;   tliey  are 
especially  well  marked  in  the  carotids,  which  closely  approach  the  large  arteries  in  structure. 


132  •  HISTOLOGY. 

smooth  muscle-fibers.  The  elastic  elements,  like  the  muscle-fibers,  pur- 
sue a  circular  course  ;  all  the  elastic  elements  of  the  media  are  united  by 
fibers  and  membranes  that  obliquely  penetrate  the  muscle  strata. 

The  externa  of  large  arteries  presents  no  essential  peculiarities  and 
differs  but  slightly  from  that  of  medium-sized  arteries.  It  does  not 
possess  the  external  elastic  membrane.  Smooth  muscle-fibers  only  occur 
in  the  externa  of  the  large  arteries  of  the  lower  animals. 

The  foregoing  classification  of  the  strata  of  the  wall  of  the  artery  corre- 
sponds to  present  usage.  There  is  a  new  proposition  to  regard  as  intima 
simply  the  epithelial  tube  alone,  as  externa  all  that  lies  outside  of  the  external 
elastic  membrane,  the  latter  to  be  reckoned  as  belonging  to  the  media.  Be- 
tween these  two  lies  the  media,  of  which  the  external  and  internal  elastic  mem- 
branes represent  the  border-lamell?e.  The  subepithelial  striated  layers  of  the 
larger  arteries  are  to  be  reckoned  as  belonging  to  the  media. 


THE    VEINS. 

There  is  no  definite  proportion  between  the  size  of  the  veins  and 
the  thickness  of  their  walls,  no  basis  for  a  division  into  groups  as  in  the 
arteries.  The  characteristic  of  the  veins  lies  in  the  preponderance  of 
the  connective-tissue  sheaths  and  in  the  slighter  development  of  the 
muscular  elements.      As  in  the  arteries  three  coats  can  be  distinguished.* 

The  bithna  consists  of  a  single  layer  of  flat  epithelial  cells,  that 
are  fusiform  only  in  the  smallest  veins,  in  others  are  polygonal  in  form. 
In  veins  of  medium  size,  having  a  diameter  of  from  two  to  nine  mil- 
limeters, layers  of  nucleated  connective  substance  follow,  that  in  large 
veins  (femoral,  popliteal,  superior  cava)  develop  into  distinctly  striped 
layers.  Following  these  is  an  internal  elastic  membrane,  which  is  struc- 
tureless in  small  veins,  in  medium-sized  and  large  veins  is  represented 
by  elastic  networks.  A  i&w  obliquely  or  longitudinally  disposed  smooth 
muscle-fibers  occur  in  the  intima  of  the  iliac,  femoral,  saphenous,  and 
mesenteric  veins. 

The  media  exhibits  great  variation.  It  is  composed  of  circular 
muscle-fibers,  elastic  networks,  and  fibrillar  connective  tissue,  and  is  best 
developed  in  the  veins  of  the  lower  extremities  (especially  in 'the  popli- 
teal), less  in  the  veins  of  the  upper  extremities,  still  less  in  the  large 
veins  of  the  abdominal  cavity  ;  finally,  it  is  absent  in  a  large  number  of 
veins  (in  those  of  the  pia  and  dura,  of  the  bones,  of  the  retina,  in 
the  superior  cava,  and  also  in  the  veins  proceeding  from  the  capillaries, 

*  Owing  to  the  meager  development  of  the  media  some  histologists  have  recognized  only- 
two  coats,  the  tunica  intima  and  the  tunica  externa,  the  layers  usually  regarded  as  tunica  media 
beins  included  in  the  latter. 


THE    CIRCULATORY    SYSTEM. 


133 


the    precapillary    vessels).       Instead   only    obliquely    and    transversely 
placed  connective-tissue  bundles  occur. 

Intima.    ^ 


Media. 


Externa. 


Internal      elastic 

^ 



membrane 

of 

ri 

y 

the  intima. 

/' 

-' 

—,~^_ 

.., Smooth 

/ 

y 

'      muscle- 

__ 

"    ...'■' 

fibers. 

S*-^,:--- 

,.  Connective 
tissue. 

Smooth  muscle-fibers  of  the  externa. 

Fig.  76. — Portion  of  Cross-section  of  a  Vein  of  a  Human  Extremity.    X  100.    Technic  No.  37. 


Intima. 


t^.^^.^'^^^vv 


-^j:^iS^' 


Media./ 


-fV 


— i.'^v    _y 
V — ^         '» .^'  '  ' .  J'  A     / 

...     •:•  ..    ^    .-^:^  rv 

Fig.  77. — Cross-section  of  a  Vein  of  a   Human  Extremity.    X  420.    The  elastic  elements  are 

stained.    Technic  No.  38. 

The  usually  well-developed  externa  consists  of  intercrossing  bun- 
dles of  connective  tissue,  of  elastic  fibers,  and  of  longitudinally  disposed 


Externa. 


134  HISTOLOGY. 

smooth  muscle-fibers,  that  are  much  more  richly  developed  in  the  veins  than 
in  the  arteries.      The  externa  of  certain  veins  (e.  g.,  of  the  trunk  of  the 

portal  and  of  the  renal  vein)  pos- 

Intima.   - — ■^rr'~l — -~-  _,_^  j^  .  ' 

Media,  j    J^"r-"~ '""'   " '"^  scsscs    a  conspicuous    and    almost 

f^%  complete    membrane   of  longitudi- 

_  ;  nally  arranged  muscle-fibers   (Fip;. 

^    -7-^'  78). 

Fig.  78.— Cross-section  of  the  Wall  of  the  The  valves  of  the  veinS  are  for- 

Renal  Vein  of  Man.    X  5°.    Technic  No.  37.  .  ^     -         .       .  , 

mations  oi  the  mtima  covered  on 
both  surfaces  by  epithelial  cells,  longitudinally  placed  on  the  side  toward 
the  blood  current,  transversely  placed  on  the  side  toward  the  vascular 
wall.  Beneath  the  longitudinally  placed  cells  lies  a  dense  elastic  net- 
work, beneath  the  transversely  placed  elements  a  delicate  fibrillar  con- 
nective tissue. 

THE    CAPILLARIES. 

The  capillaries  establish  the  communication  between  the  arteries 
and  the  veins.  There  are  a  few  exceptions,  as,  for  example,  in  the  cor- 
pora cavernosa  of  the  genital  organs.  The  transition  of  the  arteries 
into  the  capillaries  is  effected  by  a  gradual  simplification  of  the  structure  of 
the  vessel-wall  (Fig.  72  c).  The  media  becomes  steadily  thinner  and 
finally  is  represented  by  a  few  circularly  disposed  muscle-fibers  occurring 
at  wide  intervals,  that  ultimately  disappear.  The  externa  becomes 
correspondingly  attenuated  until  it  consists  of  a  thin  layer  of  connective 
tissue  containing  cells,  that  ultimately  also  disappears,  so  that  at  last 
the  only  part  of  the  vessel  wall  that  remains  is  the  intima,  the  layers  of 
which  are  likewise  reduced  until  nothing  is  left  but  a  stratum  of  plate- 
like, nucleated  epithelial  cells.  Hence  the  walls  of  the  capillaries  con- 
sist of  a  simple  layer  of  epithelial  cells,  the  form  of  which  may  be  most 
aptly  compared  with  a  steel  pen  pointed  at  both  ends.  These  cells 
are  united  at  their  edges  by  a  small  amount  of  cement  substance.  In 
a  few  places,  for  example,  in  the  capillaries. of  the  liver,  in  the  glomeruli 
of  the  kidney,  as  well  as  in  growing  capillaries,  no  cell  boundaries  can 
be  exhibited  ;  there  is  here  apparently  a  syncytium  (see  p.  73). 

The  capillaries  divide  without  decrease  in  caliber  and  by  anasto- 
mosis with  neighboring  capillaries  form  networks  differing  widely  in  the 
size  of  the  meshes.  The  closest  meshes  occur  in  the  capillary  networks 
of  secretory  organs,  for  example,  in  the  lungs  and  the  liver  ;  wide-meshed 
networks,  for  example,  in  the  muscles,  the  serous  membranes,  the 
special-sense  organs.  The  reverse  obtains  in  regard  to  the  caliber  of  the 
capillaries  ;  the  widest  capillaries  are  found  in  the  liver,  the  narrowest  in 
the  retina  and  in  the  muscles. 


THE    CIRCULATORY    SYSTEM.  135 

Development  of  capillaries. — Only  the  developmental  processes  in 
post-embryonic  epochs  will  be  considered  here.  A  conical  protoplasmic 
mass  appears  on  the  wall  of  an  existing  capillary,  resting  with  a  broad  base 
on  the  latter  and  terminating  in  a  slender,  tapering,  free  end.*  In  the 
further  course  of  development  this  pointed  free  end  unites  with  another 
approaching  off-shoot,  that  has  arisen  in  the  same  way  from  another 
point  of  the  capillary  wall.  These  formations  are  solid  at  first,  but 
gradually  become  hollow  by  the  extension  of  the  lumen  of  the  capillary, 
and  subsequently  the  walls  of  the  new  vessels  become  differentiated  to 
epithelial  cells.  The  development  of  new  capillaries  is  always  consum- 
mated in  connection  with  existing  capillaries  {cf.  technic  No.  42,  p.  153). 

All  medium  and  large  blood-vessels  possess  small  blood-vessels, 
the  vasa  vasorum,  that  provide  for  the  nutrition  of  their  walls  ;  they  run 


.®,tj 


4i. 


Fig.  79. — Surface  View  of  a  Portion  of  the  Greater  Omentum  of  a  Seven-Day-Old  Rabbit. 
c,  Blood  capillaries,  still  containing  blood  corpuscles ;  s,  capillary  sprout  tapering  to  a  free  solid  point ; 
i,  young  capillary,  the  greater  part  of  which  is  hollow,  at  s'  still  solid  ;  k,  nuclei  of  peritoneal  epithe- 
lium.    X  240.     Technic  No.  42. 

almost  exclusively  in  the  externa  (Fig.  74).     The  intima  always  is  with- 
out blood-vessels. 

On  the  walls  of  all  blood-vessels,  with  the  exception  of  the  vessels 
of  the  substance  of  the  brain  and  the  spinal  cord,  nonmedullated  and 
medullated  nerves  have  been  found,  which  form  a  plexus  in  the  tunica 
media  of  the  arteries  and  the  veins.  From  this  nonmedullated  fibers 
arise,  some  of  which  supply  the  smooth  muscle-fibers  and  some  of  which 
form  terminal  plexuses  lying  in  the  externa  and  in  the  interna  and  agree- 
ing in  all  points  with  those  of  the  heart  (p.  128).  The  capillaries  are  ac- 
companied by  encircling  networks  of  nonmedullated  nerve-fibers. 

*  Such  blind  capillary  sprouts  may  be  hollowed  out  at  an  early  period ;  corpuscles  that 
happen  to  flow  into  them  degenerate,  because  they  are  excluded  from  the  circulation  and  the 
interchange  of  gases,  and  fall  into  minute  fragments,  that  have  been  erroneously  interpreted  as 
hematoblasts ;  they  have  no  connection  with  the  true  hematoblasts  (p.  140). 


136  HISTOLOGY. 

Many  blood-vessels  are  encircled  by  lymph-vessels,  which  occa- 
sionally are  so  wide  that  they  form  spaces  completely  enclosing  the 
former,  the  "adventitial  lymph  spaces." 

The  walls  of  the  blood-vessels  permit  not  only  the  escape  of  fluid 
but  also  of  corpuscular  elements,  e.  g.  blood-cells  ;  this  is  especially  the 
case  in  the  thin-walled  veins  and  the  capillaries,  in  which  the  exit  takes 
place  betzvecn  the  epithelial  cells.  The  intercellular  spaces  thus  arising 
close  again  ;  permanent  openings,  "  stomata,"  are  not  present. 

The  glomus  caroticuin  ("carotid  gland")  is  no  gland,  but  consists 
essentially  of  blood-vessels.  The  capillaries  arising  from  the  division  of 
the  one  supplying  artery  differ  greatly  in  width  and  are  surrounded  by 
numerous  chromaffine  cells  (see  sympathetic  ganglia)  united  in  spherical 
groups,  the  so-called  secondary  nodules.  The  many  veins  collect  at 
the  periphery  of  the  gland,  that  besides  contains  fibrillar  connective  tis- 
sue, isolated  ganglion-cells,  and  conspicuous  numbers  of  medullated  and 
nonmedullated  nerve-fibers.  Similar  in  structure  is  the  coccygeal  gland 
[gloimts  coccygeiint),  the  blood-vessels  of  which  are  characterized  by 
hemispherical  evaginations. 

THE    BLOOD. 

The  blood  *  is  a  slightly  clammy,  red  liquid,  which  consists  of  a 
fluid  substance,  the  blood-plasma,  and  oi formed  elements,  the  blood-cells, 
the  blood-platelets,  and  the  elementary  granules.  The  cells  are  of  two 
kinds,  colored  and  colorless  blood-cells. 

The  colored  blood-cells  (red  blood  corpuscles,  erythrocytes,  Fig. 
80)  are  soft,  flexible,  highly  elastic  structures  and  possess  a  smooth, 
slippery  surface.  In  man  and  in  other  mammals  they  usually  have  the 
form  of  a  flat,  circular  disk,t  slightly  concave  on  each  surface,  and 
therefore  resemble  biconcave  lenses.  Exceptions  occur  in  the  llama  and 
the  camel,  in  which  the  colored  blood-cells  are  oval  disks.  Their  aver- 
age diameter  in  man  is  7.5  //.,  their  thickness  1.6//.  The  colored  blood 
corpuscles  of  domesticated  mammals  all  are  smaller  ;  the  largest  are  those 
of  the  guinea-pig  (7.48  p)  and  the  dog  (7.3  //).  The  colored  blood- 
cells  consist  of  a  stroma  (protoplasm)  which  contains  spaces  filled  with 
the  blood  coloring  substance,  the  hemoglobin.  The  hemoglobin  imparts 
to  the  blood-cells  the  yellow  or  yellowish-green  color. |     A  nucleus  and 

*  The  elements  of  the  blood  do  not  form  a  tissue,  but  represent  a  loose  union  of  element- 
ary parts,  without  definite  arrangement  of  the  same,  an  aggregation  of  cells. 

f  In  addition  there  occur  in  human  blood  spherical  colored  blood  corpuscles ;  they  are 
smaller  (5  //)  and  few  in  number. 

jOnly  when  very  many  blood-cells  He  one  over  the  other  do  they  appear  red. 


THE    CIRCULATORY    SYSTEM 


137 


an  actual  cell-membrane  are  wanting  {cf.  remark  *,  p.  140).  The  col- 
ored blood  corpuscles  of  fishes,  amphibians,  reptiles,  and  birds  are  dis- 
tinguished from  those  of  mammals  by  their  oval,  biconvex  form,  their 
generally  greater  size  (22  a  long  by  15  a  broad  in  the  frog),  as  well  as 
bv  the  presence  of  a  round  or  oval  nucleus  ;  in  other  respects  they 
exhibit  the  same  properties  as  those  of  mammals. 


Rouleau. 


Man. 

Crenated  cells. 


Froa 


Platelets 


/% 


Leucocyte  Lateral  aspect  of  colored 

in  motion  ;  at  rest.  blood-cells. 


Fig.  80. — Blood-cells.  X  600.  1,  Colored  blood-cell  seen  in  close  focus,  2,  in  distant  focus.  3,  Lateral 
aspect  of  colored  blood-cells.  4.  Colored  blood-cell,  quite  fresh,  nucleus  indistinct;  5,  the  same  cell 
a  few  minutes  later,  with  the  nucleus  plainly  visible;  6,  the  same  cell  after  treatment  with  water. 
Technics  Nos.  43,  46,  47. 


%5 


U 


The  Zi'/iiU  or  colorless  blood-cells  (leucoc}'tes)  occur  not  only  in 
the  blood  but  also  in  the  h-mph-vessel  system,  where  they  are  termed 
"  lymph  or  chyle  corpuscles."  They  are  also  found  outside  of  the  vas- 
cular systems ;  in  bone -marrow,  as  "  marrow-cells,"  and  further  in 
abundance  in  adenoid  tissue  (see  p.  95),  scattered  in  fibrillar  connective 
tissue,  and  finally  between  epithelial  and  gland-  ^^^ 

cells,  whither  they  have  wandered  by  their  power 
of  ameboid  movement ;  *  therefore  they  are  also 
called  "wandering  cells  "   (cf  pp.  68  and  93). 

In  all  cases  the  colorless  blood-cells  con- 
sist of  a  clammy  protoplasm  and  a  nucleus,  and 
are  without  a  cell-membrane.  A  definite  form 
cannot  be  described,  because  during  life  they  are 
usually  engaged  in  ameboid  activity.  In  a  state  of  rest  they  are  spheri- 
cal (Fig.  80). 

*  In  the  mucous  membranes  leucocytes  in  varying  large  numbers  wander  through  the 
epithelium  to  the  free  surface  and  there  degenerate.  In  vertebrates  this  wandering  bears  no 
relation  to  nutrient  processes  ;  on  the  other  hand,  the  leucocytes  play  a  great  role  in  preventing 
the  injurious  action  of  microbes  or  of  other  poisonous  substances. 


Fig.  Si. — Colorless  Blood- 
cells  of  Man.  a.  Lympho- 
cyte, b.  Leucocytes  with 
polymorphous  nucleus,  c. 
Leucocyte  with  neutrophile 
granules.  X  600.  Technic 
No.  45. 


130  HISTOLOGY. 

The  size  and  properties  of  the  nucleus  and  the  protoplasm  have  led 
to  the  following  classification  : 

(i)  Lymphocytes,  the  smallest  of  which  measure  from  4  to  7.5  ^. 
The  quantity  of  their  protoplasm  is  so  small  that  it  can  scarcely  be  per- 
ceived by  the  usual  methods  ;  it  forms  only  a  thin  envelope  for  the  rela- 
tively large  round  nucleus  (Fig.  ^\d).  They  exhibit  little  motility,  form 
from  22  to  25  per  cent,  of  the  leucocytes  of  the  blood,  and  are  found 
chiefly  in  adenoid  tissue.  Larger  forms,  described  as  "  large  lymphocytes," 
are  normally  found  in  youthful  blood.  (2)  Tme  leucocytes,  that  are  sub- 
divided into  several  varieties,  [a)  "  Leucocytes  with  a  polymorphous 
nucleus,"  that  is  deeply  cleft  or  lobed,  seldom  multiple.*  These  cells  have 
a  diameter  of  from  7.5  to  10  //.,  exhibit  great  motility  (the  lobulation  of 
the  nucleus  is  the  expression  of  the  motility),  and  form  the  majority 
(72  per  cent.)  of  the  leucocytes  of  the  blood.  {U)  "  Uninuclear  leuco- 
cytes," with  a  clear,  large,  round  or  oval  nucleus  and  an  abundant  proto- 
plasm free  from  coarse  granules  (Fig.  97) ;  they  may  attain  a  diameter 
of  20  fj.  and  are  scarce  (i  per  cent.)  in  human  blood.  Both  varieties  (a 
and  d)  possess  a  dense  neutrophile  granulation  (see  Technic  No.  45  c) 
and  are  united  to  each  other  by  transitional  forms.  Leucocytes  with 
polymorphous  nuclei  that  have  wandered  out  of  the  blood-vessels  into 
the  tissues  may  become  transformed  into  small  uninuclear  leucocytes. 
(^c)  "  Leucocytes  with  coarse  granules,"  from  8  to  14  /^  in  size,  with  a 
round  or  polymorphous  nucleus,  and  distinguished  by  the  possession  of 
large  quantities  of  granules,  which  react  very  differently  to  stains. 
Oxyphile  (eosinophile)  or  basophile  (=  mast-cells)  leucocytes  are  dis- 
tinguished, according  as  the  granules  imbibe  acid  or  basic  stains. f  The 
granules  probably  are  the  optical  expression  of  metabolic  processes  and 
of  phases  of  progressive  development ;  those  of  the  oxyphile  cells  are 
perhaps  albuminous  substances  taken  up  from  without  (see  further 
Technic  No.  45,  Further  treatment^ 

The  determination  of  the  proportionate  number  of,  as  Well  as  the 
ratio  between,  the  colored  and  colorless  blood-cells  is  coupled  with  con- 
siderable difficulty  and  only  approximately  correct  estimates  can  be 
given.  In  man  one  cubic  millimeter  of  blood  contains  about  5,000,000 
colored    cells.       The  white  cells  are    present    in  the    blood    in   much 

*  Multiplicity  of  nuclei  is  often  merely  apparent,  the  delicate  connecting  filaments  of  the 
deeply  cleft  nucleus  being  overlooked  ;  the  term  "poly-  (better  multi-)  nuclear"  often  used  to 
describe  leucocytes  with  polymorphous  nuclei  is  totally  inaccurate  and  should  be  discarded. 

f  Ehrlich,  who  made  this  classification,  proceeds  therein  from  other  standpoints  than  the 
chemist;  acid  dyes,  e.  g.,  are  those  in  which  the  coloring  principle  is  a  molecular  combination 
existing  chemically  as  an  acid. 


THE    CIRCULATORY    SYSTEM.  1 39 

smaller  number  ;  there  is  about  one  in  from  300  to  500  colored  blood- 
cells,  therefore  about  10,000  colorless  cells  in  one  cubic  millimeter  of 
blood. 

The  blood-platclcts  (thrombocytes)  are  very  unstable,  colorless, 
round  or  oval  disks  having  a  diameter  of  from  2  to  4  a  (Fig.  80)  ;  they 
are  capable  of  ameboid  movement  and  contain  a  body  the  nuclear  nature 
of  which  is,  however,  questionable.  At  times  they  are  present  in  the 
blood  in  large  numbers.*  Their  origin  is  obscure  ;  the  hypothesis  of 
constriction  from  erythrocytes  or  leucocytes  supported  by  some  is  dis- 
puted by  others,  likewise  is  it  still  undecided  whether  their  role  in  the 
process  of  coagulation  of  the  blood  is  direct  or  indirect. 

The  elementary  granules  are  chiefly  particles  of  fat  transferred  from 
the  chyle  to  the  blood.  They  are  easily  observed  in  the  blood  of  the 
lower  mammals  and  in  herbivorous  animals  but  are  not  normally  pres- 
ent in  the  blood  of  man.  Small  refractive  granules  not  of  a  fatty 
nature,  that  occur  in  variable  quantity  in  all  human  blood,  have  been  named 
Jiematokonia  (blood  dust). 

After  death  or  as  a  result  of  changes  within  the  vessel-wall  the 
blood  coagulates  under  the  influence  of  two  substances,  fibrinoplastin  and 
fibrinogen,  which  pass  into  solution  and  unite  in  the  plasma.  The 
product  of  this  union  \s  fibrin.  The  coagulated  blood  separates  into  two 
parts,  the  clot  and  the  scrnni.  The  clot  is  red  and  consists  of  all  the 
colored  and  the  majority  of  the  colorless  blood-cells  and  the  fibrin, 
which  microscopically  appears  as  a  felt  of  fine  fibers  ;  chemically  the 
fibers  resemble  the  fibers  of  glutinous  connective  tissue.  The  serum 
that  collects  above  the  clot  is  colorless  and  contains  a  few  colorless 
blood-cells. 

The  coloring  substance  contained  in  the  colored  corpuscles,  the 
hemoglobin,  possesses  the  property  of  crystallizing  under  certain  conditions 
and  in  nearly  all  vertebrates  the  crystals  belong  to  the  rhombic  system. 
Their  form  in  the  different  animals  varies  greatly  ;  in  man  it  is  usually 
prismatic.  Hemoglobin  is  readily  decomposed.  One  of  the  decomposi- 
tion products  is  hematin,  which  yields  Jiematoidin  and  hemin.  Cr\^stals  of 
hematoidin,  which  occur  within  the  body  in  old  extra vasated  blood,  for 
example,  in  the  corpus  luteum,  are  rhombic  prisms  of  orange-red  color. 
The  hemin  crystals,  when  well  developed,  are  rhombic  tablets  or  bars  of 
mahogany  brown  color  ;    often   they   are  very  irregular   in   form  (Fig. 


*  In  I  c.c.  of  human  blood  there  are  said  to  be  245,000  blood-platelets,  a  number  that 
probably  is  below  the  truth,  since  in  the  method  of  estimating  some  blood-platelets  always 
adhere  to  the  walls  of  the  pipet. 


140  HISTOLOGY. 

82,  i).  In  a  forensic  respect  they  are  of  great  importance  {cf.  Technic 
No.  50). 

Development  of  colored  blood-cells. — From  the  earliest  period  of 
embryonic  development  and  during  the  whole  of  life  nucleated  colored 
blood-cells,  the  liematoblasts  (erythroblasts),  are  found  in  certain  localities 
(see  bone-marrow).  Their  number  fluctuates  and  runs  parallel  with  the 
energy  of  the  blood-forming  processes.  By  indirect  division  they  give  rise 
to  the  nonnucleated  colored  blood-cells,  that  at  first  contain  a  nucleus, 
but  by  a  process  of  internal  degeneration  (not  by  extrusion)  subsequently 
lose  it.*  As  centers  for  the  formation  of  blood  in  embryonal  periods 
the  liver  and  the  lymph-glands,  later  the  spleen,  in  the  adult  exclusively 
the  bone-marrow,  must  be  indicated. 

Development  of  colorless  blood-cells. — It  is  conjectured  that  the  color- 
less blood-cells  arise  from  elements  having  their  origin  in  the  anlage  of 
the  embryonal  blood  and  blood-vessels  and  are  transported  with  (not 
in)  f  the  blood-vessels  to  the  most  diverse  localities,  to  the  anlages  of  the 


Fig.  82. — I.  Hemin  crystals  of  man;  whetstone  forms  on  the  right.  2.  Crystals  of  common  salt.  3.  Hema- 
toidin  crystals  of  man.  i  to  3  magnified  560  times.  4.  Hemoglobin  crystals  of  the  dog,  magnified  100 
times;  a,  crystal  separating  into  fibers.     Technic  No.  50. 

lymph-glands  and  lymph-nodules,  where  they  multiply  by  mitosis  and 
are  carried  back  to  the  blood  stream  through  the  lymph-vessels.  In  the 
embryonal  period  the  mother-cells  of  the  leucocytes  can  produce  not 
only  colorless  but  also  colored  blood-cells. 

In  adult  man  the  lymphocytes  are  said  to  be  formed  by  the  lymph-glands 
and  lymph-nodules,  the  leucocytes  with  polymorphous  nuclei  in  the  bone-marrow 
(hence  the  name  "myelocytes"),  statements  that  are  supported  by  clinical 
experience,  not  by  anatomic  investigations  ;  the  latter  strongly  indicate  that  the 
lymphocytes  are  juvenile  forms  from  which  the  other  varieties  of  leucocytes 
develop. 

*  Whether  the  forms  demonstrated  in  nonnucleated  elements  fixed  in  osmium  solution 
are  transformation  products,  rudiments  of  nuclei,  is  questionable,  since  it  has  been  shown  that 
similar  bodies  occur  in  the  nucleated  blood-cells. 

f  This  may  have  been  the  case  in  the  earliest  stages  ;  later  the  lymph-glands  and  nodules 
arise  from  leucocytes  that  have  migrated  from  the  blood-vessels. 


THE    CIRCULATORY    SYSTEM. 


141 


2.  The  Lymph-vessel  System. 


Valve. 


THE    LYMPH-VESSELS. 

The  wall  of  the  larger  lymph-vessels  (from  0.2  to  0.8  mm.  and  up- 
ward), like  that  of  the  blood-vessels,  is  composed  of  three  coats.  The 
intima  consists  of  epithelial  cells  and  a  network  of  delicate  elastic  fibers 
with  elongated  meshes.  The  media  is  formed  of  circularly  disposed 
smooth  muscle-fibers  and  a  few  elastic  fibers.  The  externa  consists  of 
longitudinally  arranged  bundles  of  connective  tissue,  elastic  fibers,  and 
bundles  of  smooth  muscle-fibers,  likewise  dis- 
posed in  a  longitudinal  direction.  The  wall 
of  the  smaller  lymph-vessels  and  of  the  lymph 
capillaries  is  composed  exclusively  of  ex- 
tremely delicate  epithelial  cells,  that  often 
have  sinuous  contours.  The  lymph  capilla- 
ries are  wider  than  the  blood  capillaries,  fre- 
quently are  beset  with  constrictions  and  dila- 
tations, and  where  they  branch  are  often 
considerably  expanded ;  the  networks  they 
form  are  more  irregular. 

The  question  of  the  origin  of  the  lymph- 
vessels  is  not  yet  satisfactorily  decided;  while 
some  authors  are  of  the  opinion  that  the 
lymph  capillaries  form  a  closed  system,  ac- 
cording to  another  widely  entertained  view 
the  lymph  capillaries  are  open  toward  the 
periphery  and  in  direct  connection  with  the  sys- 
tem of  intercommunicating  cell-spaces  of  con- 
nective-tissue (juice-canal-system,*  p.  100). 

According  to  the  first  theory  the  nutritive  fluids  (tissue  juices) 
passed  through  the  walls  of  the  blood  capillaries  that  are  not  used  in  the 
nutrition  of  the  tissues  penetrate  the  closed  lymph  capillaries  by  endos- 
mosis  ;  according  to  the  second  view  the  tissue  juices  flow  directly  from 
the  tissues  into  the  patent  orifices  of  the  lymph  capillaries. 

It  is  said  that  the  lymph-vessels  of  the  pleura  and  of  the  peritoneum  are 
in  open  communication  with  their  respective  cavities  through  small  openings, 
the  stomata,  between  the  epithelial  cells,  which  in  the  pleura  are  found  at  the 


Fig.  S3. — Lymph-vessel  of  the 
Mesentery  of  a_  Rabbit, 
showing  the  boundaries  of  the 
epithelial  cells.  X  50.  Techiiic 
No.  40. 


*The  juice  canaliculi  are  designated  lymph  canaliculi  in  contradistinction  to  lymph- 
vessels  provided  with  cellular  walls  ;  other  authors  make  lymph  canaliculi  equivalent  to  lymph- 
vessels  plus  the  tissue-juice  canal  system. 


142 


HISTOLOGY. 


intercostal  spaces  and  in  the  peritoneum  on  the  central  tendon  of  the  dia- 
phragm. However,  it  is  a  question  whether  the  stomata  described  in  mam- 
mals are  not  artifacts.  Stomata  are  unnecessary  in  the  transfer  of  fluids 
and  corpuscular  elements  from  the  peritoneal  cavity  into  the  lymph-vessels, 
because  thin-walled  lymph-vessels  lie  immediately  beneath  the  peritoneal 
epithelium. 

THE    LYMPH-GLANDS. 

The  lymph-glands  (lympho-glandulae,  lymph-nodes)  are  macroscopic 
bodies  intercalated   in  the  course  of  the  lymph-vessels.      Usually  they 


Capsule. 


Sinus. 


Trabeculee. 


Cortical 
substance. 


Medullary 
substance. 


Germinal 

center  of  a 

secondary 

nodule. 


% 


Fat. 


Fig.  84.— Longitudinal  Section  of  a  Human  Cervical  Lvivihh-cland.    X  12.    Technic  No.  53. 

are  rounded  oval  or  flat,  kidney-shaped  structures  and  differ  greatly  in 
size.  On  one  side  there  is  often  a  scar-like  depression,  the  hilus,  at  which 
the  efferent  lymph-vessels  emerge.*      Their  construction  becomes  intelli- 

*  The  afferent  lymph-vessels  penetrate  the  gland  at  various  points. 


THE    CIRCULATORY    SYSTEM.  I43 

gible  if  we  proceed  from  the  following  conception  :  In  certain  localities 
from  three  to  six  lymph-vessels  divide  repeatedly  into  anastomos- 
ing branches,  which  soon  reunite  into  the  same  or  a  lesser  number  of 
usually  narrower  lymph-vessels.  In  this  way  a  kind  of  rete  mirabile  *  is 
formed.  The  dividing  lymph- vessels  are  called  afferent  vessels  (vasa 
afiferentia),  the  reuniting,  efferent  vessels  (vasa  efferentia).  Within  the 
meshes  of  this  reticulum  lie  some  spherical  and  some  elliptical  bodies, 
that  consist  of  adenoid  tissue.  The  spherical  bodies,  the  secondary 
nodules  (follicles,  ampullae),  occupy  the  periphery,  the  elliptical  bodies, 
the  vtediillary  cords,  the  center  of  the  lymph-gland.  The  lymph-gland 
is  enveloped  in  fibrous  connective  tissue,  the  capsule,  which  sends  pro- 
cesses, the  trabccuhr,  into  the  interior  of  the  organ  (Figs.  84  and  85). 
Fine  extensions  from  the  trabeculae,  in  the  form  of  reticular  connective 
tissue,  pierce  the  walls  of  the  lymph-v^essels,  penetrate  the  secondary 
nodules  and  the  medullary  cords,  and  form  a  support  for  the  numerous 
leucocytes  found  there. 

Accordingly  the  lymph-gland  consists  of  a  cortical  and  a  medullary 
substance,  the  relative  proportions  of  which  vary  greatly.  The  cortical 
substance  contains  the  secondary  nodules,  which  continue  centralward 
directly  into  the  medullary  cords  (Figs.  84and85).  The  secondary  nodules 
and  the  medullary  cords  are  surrounded  by  the  continuations  of  the 
afferent  lymph-vessels. f  The  latter  here  are  greatly  expanded  and  are 
termed  lymph  sinuses  ;  they  are  pierced  by  the  connective-tissue  reticu- 
lum. The  secondary  nodules  and  the  medullary  cords  are  composed  of 
adenoid  tissnc,  that  is,  of  reticular  connective  tissue  the  meshes  of  which 
are  crowded  with  leucocytes.  In  many  of  the  secondary  nodules  there 
is  at  times  a  light,  spherical  spot,  the  germinal  center,  in  which  karyoki- 
netic  figures  are  always  to  be  found. ;{;  The  secondary  nodules  are 
stations  for  the  formation  of  leucocytes,  which  pass  into  the  lymph- 
sinuses  and  thence  into  the  vasa  efferentia. 

The  capsule  consists  of  fibrous  connective  tissue  and  elastic  fibers, 
in  a  variable  quantity  increasing  with  age,  also  smooth  muscle-fibers, 
which  in  the  large  lymph-glands   of  the  ox  are  united  in  large  strands. 

*  Retiamirabilia  were  first  described  in  connection  with  the  blood-vessels.  They  consist  of 
a  vascular  plexus,  which  sitddenly  interrupts  the  course  of  the  vascular  stem.  They  occur  in 
the  course  of  both  arteries  and  veins,  and  accordingly  there  are  arterial  and  venous  retia 
mirabilia.  The  glomeruli  of  the  kidneys  are  exquisite  examples  of  such  arterial  vascular 
networks  icf.  Fig.  247)  :  a  small  arterial  stem  divides  into  capillary  twigs,  which  in  turn 
reunite  to  a  small  arterial  stem,  which  then  ramifies  in  the  usual  way. 

T  The  lymph-vessels  never  penetrate  the  interior  of  the  secondary  nodules. 

%  Multiplication  of  cells  also  occurs  in  the  medullary  cords,  but  in  much  slighter  degree 
than  in  the  secondary  nodules. 


144 


HISTOLOGY. 


The  trabecJilcB  have  the  same  structure  ;  they  pass  between  the  secondary- 
nodes  and  the  medullary  cords,  but  do  not  come  into  contact  with  them, 
being  separated  from  them  by  the  lymph-sinus.  The  wall  of  the 
lymph-sinus  is  formed  of  only  a  simple  layer  of  plate-like  cells  ; 
similar  cells  clothe  the  surface  of  the  secondary  nodules  and  the  medul- 
lary cords,  and  also  the  surface  of  the  trabeculae  and  of  the  connective- 
tissue  reticulum  [cf.  p.  94). 

The  structure  of  the  lymph-glands  here  described  is  difficult  to 
recognize,  owing  to  sundry  complications.  These  complications  consist 
in  :  (i)  the  frequent  merging  of  neighboring  secondary  nodules  with  each 
other  ;  (2)  the  union  of  the  medullary  cords  in  the  form  of  a  coarse  net- 

Capsule.      Secondary  nodule  ("  follicle  ").        Blood-vessel. 

^  /' 

\  I 


Trabecula. 


'% 


% 


I 

Hilus.        Medullary  cord.        Lymph-sinus. 
Fig.  85. — Section  of  a  Lymph-gland  of  a  Rabbit.    X  28.    (Schaper.)    Technic  No.  53. 


work  ;  (3)  the  similar  network  formed  by  the  trabeculae  ;  (4)  the  interlac- 
ing of  the  networks  formed  by  the  medullary  cords  and  the  trabeculae  (Fig. 
86)  ;  (5)  the  presence  of  leucocytes  in  the  lymph-sinus,  which  must  first 
be  removed  by  special  methods.*  In  this  manner  the  secondary  nodules, 
the  medullary  cords,  and  the  leucocytes  in  the  lymph-sinus  form  a  soft 
mass,  that  has  been  named  the  pulp  or  parenchyma  of  the  lymph-gland. 
The  majority  of  the  blood-vessels  enter  at  the  hilus,  the  others  at 
various  points  on  the  surface  of  the  gland.  The  latter  are  delicate 
vessels  and  divide  in  the  capsule  and  in  the  large  trabecule,  in  the  axis 


*  Editor'' s  remark  :  In  preparations  of  lymph-glands  it  is  necessary  to  dislodge  the  leuco- 
cytes to  bring  the  lymph-sinus  into  view  (see  Technic  No.  53). 


THE    CIRCULATORY    SYSTEM. 


145 


of  which  they  run.  The  large  artery  entering  at  the  hilus  divides  into  a 
number  of  branches,  that  here  are  surrounded  by  richly  developed  connec- 
tive tissue.  The  branches  are  principally  distributed  to  the  adenoid  tissue, 
only  a  few  entering  the  trabeculse  ;  they  pass  through  the  l\'mph-sinuses, 
into  the  medullary  cords,  then  into  the  secondary  nodules,*  and  in  both 
situations    break    up   into    richly   developed    capillary   networks   which 


^s^. 


"TV" 


f-^J 


-«^5r^ 


Trabeculje.  r- 


Medullary 
cords.  ' 


Plate-like 
cells. 


'  if  r^V  V  9  *jr 

^^-j'i ... 

ftS 


:h 


Fig.  S6.     X  io.  Fig.  87.    X  240. 

From  a  \'ertical  Sectio.n  of  a  Lymph  Gland  of  an  Ox.  The  medullary  substance.  In  the  upper 
half  the  medullary  cords  and  trabeculae  are  cut  through  longiludinally,  in  the  lower  half  trans- 
versely. Both  form  a  continuous  network.  In  the  lymph-sitius  the  delicate  fibers  of  the  reticular 
connective  tissue,  still  containing  a  few  leucocytes,  can  be  seen.  Drawn  with  change  of  focus. 
Technic  No.  55. 

supply  the  oxygen  needed  in  the  formation  of  the  leucocytes.     The  veins 
emerge  at  the  hilus. 

The  few  nerves  of  the  lymph-glands  are  partly  medullated,  partly 
nonmedullated  bundles  of  fibers,  that  chiefly  form  richly  branched 
plexuses  about  the  blood-vessels  ;  nerves  have  been  found  in  the  capsule 
and  in  the  trabeculae,  but  not  in  the  nodules. 


THE    PERIPHERAL    LYMPH    NODULES. 
(NoDULi   Lymphatici.) 

Reticular  connective  tissue  enclosing  leucocytes  is  not  confined  to  the 
lymph-glands  ;  it  occurs  in  great  diffusion  in  many  mucous  membranes 

*  The  arteries  entering  into  the  axis  of  the  secondary  nodules  break  up  in  slender  non- 
anastomosing  capillaries,  which  pass  into  a  meshwork  of  venous  capillaries  lying  at  the  border 
of  the  nodule,  from  which  larger  veins  arise.  The  conditions  here  are  quite  like  those  in  the 
spleen. 


146  ■    HISTOLOGY. 

and  in  different  degrees  of  development,  sometimes  as  diffuse,  sometimes 
as  definitely  cit'cumscribed  infiltrations  of  leucocytes.  These  formations 
are  not  included  in  the  lymphatic  system.  But  more  highly  developed 
structures,  nodules  with  germinal  centers,  closely  resembling  the  secon- 
dary nodules  of  the  lymph-glands,  are  also  found  in  the  mucous  mem- 
branes ;  these  are  ndsn&d  peripheral  lymph  nodules  and  are  included  in  the 
lymphatic  system.  They  occur  in  many  mucous  membranes  isolated,  as 
the  solitary  nodides  (solitary  follicles),  or  grouped,  as  the  agminated 
nodules  (Peyer's  patches),  and  always  lie  in  a  simple  layer  in  the  tunica 
propria  close  beneath  the  epithelium  (see  Organs  of  the  Digestive  System). 
The  number  and  distribution  of  the  peripheral  lymph  nodules  are  subject 
to  considerable  fluctuation,  not  only  in  the  different  species  of  animals,  but 
in  different  individuals  ;  since  their  mass  also  varies  and  frequent  transi- 
tions to  circumscribed  and  to  diffuse  infiltrations  exist  it  is  highly  prob- 
able that  they  are  temporary  structures  that  arise  and  disappear  during 
life.  They  are  distinguished  from  the  true  lymph-glands  above  all  by 
their  less  intimate  relation  to  the  lymph-vessels,  which  do  not  form  an 
encircling  sinus  for  the  foUicle.*  But  the  possession  of  a  germinal  center, 
a  brooding  place  for  young  leucocytes,  appears  in  so  far  to  entitle  them 
to  a  place  in  the  lymph  vascular  system.  The  young  leucocytes  only 
in  part  enter  the  lymph-vessels  ;  many  wander  through  the  epithelium  to 
the  surface  of  the  mucous  membrane  {cf.  remark  *,  p.  137). 

THE   LYxMPH. 

The  lymph  is  a  colorless  fluid  in  which  leucocytes  [cf.  white  blood- 
cells,  p.  137)  and  granules  are  suspended.  The  latter  are  immeasurably 
small,  consist  of  fat,  and  are  principally  found  in  the  lymph  (or  chyle) 
vessels  of  the  intestine  ;  frequently  they  are  present  in  colossal  quantity 
and  then  they  impart  the  white  color  to  the  chyle.  In  other  lymph-ves- 
sels the  fatty  granules  occur  sparingly.  In  the  lymph-glands  many 
leucocytes  are  found  in  which  the  envelope  of  protoplasm  surrounding 
the  nucleus  is  so  thin  that  its  presence  can  only  be  demonstrated  with 
high  magnifications. 

THE    SPLEEN. 

The  spleen  is  an  organ  closely  alHed  to  the  blood-lymph-glandsf 
and  consists  of  a  capsule,  of  trabeculae,  and  of  the  pulp. 

*  The  only  exception  exists  in  the  rabbit,  in  which  the  sinus  occurs  in  the  agminated 
nodules  ;  on  the  other  hand,  in  the  solitary  nodules  of  this  animal  the  sinus  is  likewise  wanting. 

f  In  some  mammals,  e.  g.  in  the  pig,  lymph-glands  of  a  dark  red  color,  similar  to  that 
of  the  spleen,  occur  along  the  thoracic  aorta ;  they  are  characterized  by  the  absence  of  efferent 
and  afferent  lymph-vessels  and  in  being  penetrated  only  by  blood-vessels,  which  take  up  the 
leucocytes  formed  in  the  gland.  Such  "  blood-lymph  glands"  also  occur  in  man,  in  the  tissue 
between  the  vessels  of  the  kidney. 


THE    CIRCULATORY    SYSTEM. 


147 


The  capside  is  firmly  united  by  growth  to  the  peritoneum  which 
covers  it  and  consists  of  tough  fibrous  connective  tissue,  a  few  smooth 
muscle-fibers,  and  dense  nets  of  elastic  fibers,  the  quantity  of  which 
increases  with  age.  From  the  capsule  numerous,  mostK'  cord-shaped 
processes,  the  trabecule^,  pass  into  the  interior  of  the  spleen  and  form  a 
continuous  network  ;  they  likewise  consist  of  connective  tissue,  of  elas- 
tic fibers,  and  in  man  of  a  few,  in  animals  [e.  g.  the  dog  and  the  cat)  of 
an  abundance  of  smooth  muscle-fibers.  The  thicker  trabeculse  contain 
the  larger  ramifications  of  the  blood-vessels.    The  meshes  of  the  trabec- 


Spleen  sinus. 


Sheathed  artery.        Pulp  artery. 


Pulp-vein 


Beginning  of  a 
trabecular  vein 


Capillaries  of 

a  nodule 


Central  artery. 


Trabecular  vein 


Trabecular 
arterv 


i^^   •    \     I  Spleen 
•'•^'i:'»\K    ?-     >     lobule. 


Hilu 


Reticulum.      Spleen  11 


Capsule. 


Fig.  SS.— Scheme  of  the  Human  Spleen,  x,  opening  of  the  arterial  capillaries  in  theispleen  sinus. 
XX,  interruption  of  the  closed  blood  course  at  the  ends  of  the  arterial  capillaries,  at  the  margin  of 
the  nodule,  xxx.  (For  the  sake  of  distinctness  the  spleen  sinus  is  sketched  too  far  removed  from 
the  margin  of  the  nodule.) 

ular  network  are  filled  with  the  pitlp,  a  red,  soft  mass  consisting  of  ade- 
noid tissue  and  the  smaller  blood-vessels,  the  minute  structure  of  which 
will  be  considered  after  the  description  of  the  arrangement  of  the  blood- 
vessels. 

The  arteries  entering  at  the  hilus  divide  into  branches,  which  further 
on,  together  with  the  veins,  are  enclosed  in  the  trabeculse  (Fig.  Z?i). 
Then  the  arteries  separate  from  the  veins  and  the  tunic  derived  from  the 
trabecul^e,  the  "  adventitial  sheath,"  as  well  as  the  tunica  externa  become 
loosened  by  infiltration  with  numerous  leucocytes.     These  masses  of  leu- 


148 


HISTOLOGY. 


oocytes  may  accompany  the  artery  in  its  entire  course  as  a  continuous  la}^er 
(£'.  g-.  in  the  guinea-pig)  or  may  be  confined  to  a  few  locaHties  (^e.  g.  in 
man,  the  cat,  etc.).  In  the  latter  case  the  leucocytes  form  spherical  masses 
of  from  0.2  to  o.y  mm.  in  size,  the  spleen  nodules  (Malpighian  corpus- 
cles), or  slender  spindles. 

The  spleen  nodules  are  usually  situated  in  the  forks  of  the  smaller 
arteries,  in  such  a  manner  that  the  artery  pierces  the  middle  or  the  edge  of 
the  nodule.  For  this  reason  these  arteries  are  called  central  arteries ; 
they  send  off  capillaries  which  are  well  developed  in  the  nodules,  but  only 


Spleen  sinus. 


Arterial  capil- 
laries (con- 
tinuing into  a 
sinus). 


Vein. 


Artery. 


Trabecula. 


'If, 


T'l 


Transition   of    a 
sinus  into  a — 


Vein. 

Spleen  nodule. 
?  Spleen  pulp. 


■^^-^^ 


Fig.  89. — Section  through  the  Injected  Spleen  of  a  Cat.    The  spleen-sinus  is  wider  in  the  cat  than 

in  man.     Technic  No.  59. 


slightly  in  the  spindles.  The  slender,  nonanastomosing  terminal  branches 
of  the  arteries,*  the  socalled  pulp  arteries,  shortly  before  their  transi- 
tion into  capillaries  are  provided  with  relatively  thick  walls  and  are  called 
sheathed  rtr^'^r/£'j-("  ellipsoids  ");  the  arterial  capillaries  arising  from  them 
empty  at  narrow  angles  into  wide  spaces  (from  12  to  40  //),  the  spleen 
sinuses, t  which  by  means  of  wide  pulp  veins  are  connected  with  the  large 
veins  running  in  the  trabeculae. 

According  to  the  foregoing  description  the  blood-vessel  system  of  the 
spleen  is  closed  on  all  sides ;  but  recent  researches  support,  with  much  inge- 
nuity, the  theory  advanced   long  since,  that  the  path   of  the   blood  is   inter- 


*In  injected  and   macerated   spleens  the  pulp  can  be  washed  out,  and  then  the  slender 
terminal  branches  of  the  arteries  can  be  seen  lying  together  in  a  leash  or  pencil  (penicillus). 
-f"  Synonyms  :    "  ampullas,"  "  venous  capillaries,"    "  intermediate  lacunse." 


THE    CIRCULATORY    SYSTEM. 


149 


rupted.  This  interruption  occurs  at  the  edge  of  the  nodule  and  at  many 
all)  terminals  of  arterial  capillaries,  by  the  breaking  up  of  the  capillary 
The  blood  then  passes  into  the  reticu- 
lum of  the  pulp  and  is  transferred  from 
here  through  delicate  tubules  into  the 
spleen  sinuses.  This  satisfactorily 
explains  the  fact  that  free  erythro- 
cytes occur  in  the  pulp.  On  this 
theory  the  path  of  the  blood  in  the 
spleen  must  be  regarded  as  partly 
closed  and  as  partly  interrupted  or 
"  open." 


Capsule.    . 


Trabeculae.    — - 


Tnot 
wall. 


Spleen  nodules. 


Pulp. 


Trabeculae. 


IP 

m 


By  splee7i  pulp  is  understood 
the  mass  of  vascular  ramifications 
external  to  the  trabeculae  and  the 
tissue  lying  between  the  ramifica- 
tions. The  pulp,  also  designated 
"parenchyma"*  and  "  red  pulp," 
forms  a  network  of  cords  which  sim- 
ilarly to  that  of  the  lymph-glands, 
lies  in  the  meshes  of  the  trabecular 
net.  The  pulp-cords  are  occasion- 
ally connected  with  the  nodules  and 
consist  of  very  delicate  reticular 
connective  tissue  (p.  94)  and  nu- 
merous cellular  elements.  The  latter  are  in  part  leucocytes,  in  part 
somewhat  larger  multinucleated  cells,  also  cells  containing  erythrocytes 


Artery. 


Fig.  90.— From  a  Cross-section  of  a  Human 
Spleen,  showing  well-developed  spleen  nod- 
ules, the  majority  of  which  are  pierced  ec- 
centrically by  an  artery.  The  right  branch  of 
the  arterv  has  a  spindle-shaped  accumulation 
of  leucocytes.     X  lo.     Technic  No.  57. 


Fig.  91. — Elements  of  the  Human  Spleen. 
X  560.  1.  Colorless  blood-cells.  2.  Epithelial 
cells.  3.  Erythrocytes.  4.  Cells  containing 
granules;  the  upper  one  enclosing  also  an 
erythrocyte,  b.  Technic  No.  56. 


Fig.  92.— Reticular  Connective  Tissue  of  the 
Human  Spleen.  X  560.  Sketched  from  the 
edge  of  a  shaken  preparation.     Technic  No.  58. 


(Fig.  91)  and  free  erythrocytes.     A  granular  pigment  is  also  found  in 


*  By  the  name  "  parenchyma  "  (that  poured  in  between),  earlier  authors  designated  the 
masses  of  tissue  lying  between  the  blood-vessels  in  the  most  widely  difterent  organs.  It  is  still 
customary  to  speak  of  the  parenchyma  of  the  liver,  the  lungs,  etc. 


ISO 


HISTOLOGY. 


the  pulp.  The  nodules  agree  in  minute  structure  with  the  secondary 
nodules  of  the  lymph-glands  ;  occasionally  they  even  contain  germinal 
centers  and  usually  delicate  elastic  fibers.  The  nodules  and  spindles  of 
the  spleen  belong  to  the  temporary  lymphatic  structures  ;  continually 
some  undergo  regressive  change  and  new  ones  develop. 

The  portion  of  the  blood-vessels  designated  sheathed  or  ellipsoid 
artery  measures  only  from  0.15  to  0.25  mm.  and  has  a  peculiar  struc- 
ture ;  the  vascular  epithelium  is   surrounded  by  a  thick  layer  of  longi- 


^^  #%^  >^: 


Migrating 

leucocyte. 


■~  -^  -__  __^  Spleen 

sinuses. 


•'  ) 


|U  "~"-~—__^  Erythrocytes. 


Fig.  93.— Portion  of  a  Thin  Section  through  a  Human  Spleen.     X  600.    Technic  No.  57. 


tudinally  disposed  fibers  resembling  the  striped  connective  substance  of 
the  medium-sized  arteries  *  (p.  129).  Quite  individual  are  the  epithelial 
cells  of  the  spleen  sinuses,  the  socalled  spleen  fibers,  slender  forms  (Fig. 
91,  2),  probably  capable  of  contraction,  with  very  prominent  nuclei  that 
protrude  toward  the  lumen  ;  they  rest  upon  a  thin  membrane  and  are 
not  in  contact  with  one  another  at  their  edges.      Here  numerous  leuco- 

*The  constant  diameter  (from  6  to  8  ^)  of  the  sheathed  arteries  suggests  that  they  serve 
to  regulate  the  arterial  blood  stream,  by  preventing  a  too  precipitate  flooding  of  the  sinuses  and 
the  parenchyma.  They  are  very  strongly  developed  in  animals,  e.  g.  in  the  porcupine,  the  dog, 
and  the  pig. 


THE    CIRCULATORY    SYSTEM. 


151 


cytes  may  be  seen  wandering  through  the  wall  of  the  sinus  (Fig.  93). 
The  walls  of  the  sinuses,  like  those  of  the  veins  that  follow,  are  kept 
open  by  ring-Hke  strands,  that  are  not  elastic  in  nature,  but  resemble 
reticular  connective  tissue.  The  larger  veins,  wholly  or  partially  en- 
closed in  the  trabeculae,  possess  no  proper  wall  except  their  epithelium. 
The    spleen  venous   blood  is   rich    in    leucocytes  (70  times   richer  than 


Surface  blackened 
by  precipitates 
of  silver. 


Small  nervi- 
bundle. 


Branches  for  the  ,. 
arterial  wall. 


■:!:.:y 


Fig.  94.— Section  of  the  Spleen  of  a  Mouse.  X  85.  The  boundary  between  the  spleen  pulp  and  the 
artery,  the  sheath  of  which  is  infiltrated  in  its  entire  length  with  leucocytes,  is  indicated  by  a  dotted 
line.     Technic  No.  60. 


spleen  arterial  blood)  that  have  come  through  the  patent  beginnings 
of  the  veins,  as  well  as  through  the  walls  of  the  sinuses. 

The  lymph-vessels  are  profuse  on  the  surface  of  the  spleen  of  ani- 
mals, but  in  man  are  only  slightly  developed.  Deep  lymph-vessels, 
running  in  the  interior  of  the  spleen,  are  wanting. 

The  nerves  consist  of  a  few  medullated  fibers  and  many  naked  axis- 
cylinders.     They  enter  the  spleen   with    the   arteries   and   ramify   with 


152  HISTOLOGY. 

them.  During  their  course  they  send  branches  to  the  musculature  of 
the  arteries  (Fig.  94)  and  to  the  trabeculae.  Plexuses  of  nonmedullated 
nerve-fibers  are  also  found  in  the  spleen  pulp  ;  they  are  partly  sensory  in 
nature  and  probably  arise  from  the  ramifications  of  the  medullated  fibers 
just  mentioned. 

The  uninjured  external  surface  of  the  spleen  frequently  shows  boundary 
marks  of  spheric  lobules ;  the  attempt  to  find  a  division  into  lobules  in  sections 
through  the  human  spleen  cannot  be  definitely  carried  out;  though  always 
near  the  surface  of  the  spleen  trabeculae  with  their  enclosed  veins  can  be  re- 
garded as  boundaries  of  lobules  and  that  the  arteries  are  situated  in  the  axis  of 
the  lobule,  as  far  as  possible  from  the  ''interlobular  "  trabecular  veins,  can  be 
shown  {cf.  scheme  of  Fig.  88).  In  the  depths  of  the  spleen  a  division 
into  lobules  is  impossible. 

TECHNIC. 

No.  37. — The  heart  and  the  large  blood-vessels. —  Cut  a  papillary 
muscle  from  a  human  heart,  a  piece  of  the  aorta  2  cm.  square,  a  piece  i 
or  2  cm.  long  of  the  brachial  artery  with  its  veins  and  the  enveloping 
connective  tissue,  a  piece  of  the  renal  vein  i  cm.  long,  and  suspend 
them  on  a  thread  in  a  bottle  containing  40  c.c.  of  absolute  alcohol. 
After  twenty -four  or  forty-eight  hours  the  objects  are  ready  to  section. 
Embed  them  in  liver  (the  artery  and  vein  may  be  embedded  together 
and  will  not  be  injured  by  strong  compression),  cut  thin  cross-sections, 
stain  them  in  Hansen's  hematoxylin,  from  two  to  five  minutes  (p.  38), 
and  mount  in  xylol-balsam  (Fig.  70,  71,  74,  75,  78).  The  elastic  fibers 
remain  unstained,  but  can  be  distinctly  recognized,  often  only  with  high 
powers. 

The  arrangement  of  the  elements  of  the  externa  cannot  be  satis- 
factorily appreciated  in  cross-sections  ;  often  all  appear  to  be  circularly 
disposed  (a  portion  have  a  circular  arrangement,  for  example,  those 
of  the  innermost  stratum  of  the  external  elastic  membrane).  The  exact 
arrangement  can  be  seen  only  in  longitudinal  sections,  which  also  show 
the  muscle-fibers  of  the  externa  plainly. 

No.  38. — Elastic  fibers  of  the  blood-vessels. — Stain  objects  fixed  in  ab- 
solute alcohol  according  to  No.  37,  with  borax  carmine  and  with  resorcin 
fuchsin  (p.  43)  and  mount  in  xylol-balsam.  Result :  similar  to  figure 
yy,  that  preparation  having  been  stained  with  the  less  efficient  orcein. 

No.  39. — Small  blood-vessels  and  capillaries. — From  the  base  of  a 
human  brain  slowly  strip  off  pieces  of  the  pia  from  i  to  3  cm.  long  (in 
this  way  delicate  blood  vessels  that  penetrate  the  brain  vertically  are 
withdrawn),  shake  them  in  distilled  water  to  free  them  from  adherent 
fragments  of  brain  tissue,  and  place  them  in  60  c.c.  of  Zenker's  fluid 
(p.  33)  for  one  hour  ;  wash  them  for  one  hour  in  running  water,  and 
harden  them  in  about  40  c.c.  of  gradually  strengthened  alcohols  (p.  35). 
Examine  one  of  these  pieces  in  a  watch-glass  on  a  black  background 
and  it  will  be  seen  that  small  vessels  are  isolated. 


THE    CIRCULATORY    SYSTEM.  I  53 

(a)  With  a  fine  scissors  cut  off  small  twigs  with  their  ramifications, 
stain  them  for  from  two  to  five  minutes  in  Hansen's  hematoxylin  (p.  38) 
and  mount  in  balsam  *  (Fig.  72). 

{b)  From  the  larger  twigs  of  the  cerebral  blood-vessels  cut  pieces 
about  5  mm.  long,  slit  them  open  lengthwise,  stain  them  in  Hansen's 
hematoxylin,  and  place  them  on  a  slide  with  the  externa  side  down. 
Mount  in  balsam.  By  changing  the  focus  the  three  coats  of  the  vessel 
and  their  general  arrangement  can  be  seen. 

Capillaries  can  be  found  on  examining  fresh  brain  tissue.  They 
are  recognized  by  their  parallel  outlines  and  the  oval  nuclei  of  their 
epithelial  cells  ;  they  are  also  found  in  other  preparations,  for  example 
in  technic  No.  9,  p.   102. 

No.  40. — Epitheliuui  {cndotluiiiiui)  of  the  blood-vessels. — Decapitate 
a  rabbit,  open  the  abdomen  by  a  crucial  cut  made  with  the  scissors  ; 
insert  a  cork  frame  about  2  cm.  square  under  the  mesentery,  span  the 
membrane  smoothly  and  fasten  it  with  quills  or  hedgehog  spines,  taking 
care  to  touch  it  as  little  as  possible.  Cut  around  the  frame  and  place 
the  stretched  membrane  with  tlie  frame  in  20  or  30  c.c.  of  i  per  cent, 
silver-nitrate  solution.  In  about  thirty  seconds  the  solution  becomes 
turbid  and  milky  ;  remove  the  frame,  carefully  wash  the  membrane  with 
distilled  water,  place  the  whole  in  a  white  capsule  containing  100  c.c.  of 
distilled  water  and  expose  it  to  direct  sunlight.  In  a  few  minutes  a 
brown  coloration  appears.  Now  transfer  the  whole  to  50  c.c.  of  70  per 
cent,  alcohol  (the  membrane  must  be  submerged  in  the  alcohol) ;  in  a 
half-hour  cut  out  small  pieces  5  or  10  mm.  long  and  mount  them  in 
xylol-balsam.  In  the  absence  of  sunlight  take  the  preparation  from  the 
silver  solution,  wash  it,  place  it  for  about  twenty  hours  in  30  c.c.  of  70 
per  cent,  alcohol,  then  in  a  like  quantity  of  90  per  cent,  alcohol,  and 
expose  it  to  sunlight  on  the  first  opportunity.  It  must  not  be  forgotten 
that  the  whole  blood-vessel  and  not  a  section  of  it  is  present,  so  that  in 
order  to  obtain  a  view  such  as  that  in  Fig.  73  the  surface  of  the  vessel 
must  be  in  focus. 

No.  41. — Elastic  fenestrated  vieuibranes. — See  Technic  No.  15,  P- 
103. 

No.  42. — Development  of  capillaries. — Chloroform  a  seven-day-old 
rabbit,  fasten  it  with  pins  on  a  cork  plate,  open  the  abdomen  by  a  crucial 
incision,  quickly  remove  the  spleen,  stomach,  and  attached  greater  omen- 
tum and  place  these  parts  in  80  c.c.  of  a  saturated  aqueous  solution  of 
picric  acid  (p.  22).  In  this  solution  the  omentum,  otherwise  difficult  to 
separate,  spreads  out  easily.  After  one  hour  cut  it  off,  transfer  it  to 
60  c.c.  of  distilled  water,  and  divide  it  with  the  scissors  into  pieces  about 
I  cm.  square.  Place  such  a  piece  on  a  dry  slide,  remove  the  water  with 
filter-paper,  and  with  needles  spread  it  out  as  smooth  as  possible,  which  is 

*  Frequently  the  blood-vessels  are  filled  with  blood-cells,  which  make  an  exact  study  of 
the  vascular  wall  more  difficult ;  this  obstacle  can  be  removed  by  placing  the  fresh  blood-vessels 
in  distilled  water  for  an  hour.      In  this  way  the  cells  are  decolored  {cf.  technic  No.  43"). 


1 54  HISTOLOGY. 

the  more  easily  done  the  less  moisture  there  is  present.  Put  one  or  two 
drops  of  Hansen's  hematoxylin  on  the  preparation.  In  from  one  to  five 
minutes  drain  off  the  hematoxylin  and  place  the  slide  with  the  preparation 
in  a  flat  dish  containing  distilled  water  ;  the  membrane  will  soon  float 
from  the  slide  and  will  remain  smooth,  and  in  five  minutes  should  be 
transferred  to  a  watch-glass  containing  eosin  (p.  39),  in  which  it  should 
remain  three  minutes.  It  should  then  be  washed  for  one  minute  in  dis- 
tilled water  and  placed  on  a  slide ;  the  water  should  be  absorbed  with  filter- 
paper,  any  wrinkles  smoothed  out  with  needles,  and  a  cover-glass  with  a 
drop  of  dilute  glycerol  suspended  from  its  lower  surface  applied.  The  prep- 
aration may  be  mounted  in  balsam  instead  of  glycerol  (that  is,  dehydrated 
in  95  per  cent,  alcohol,  cleared  in  carbol-xylol,  and  then  mounted  in 
xylol-balsam),  but  the  finer  structural  details  are  apt  to  be  lost.  The 
colored  blood  corpuscles  are  stained  a  bright  red  by  the  eosin  (Fig.  79). 
In  spreading  the  membrane  on  the  slide  delicate  young  capillaries 
maybe  easily  torn  from  the  older  capillaries  and  then  simulate  "isolated 
cells  containing  blood  corpuscles  "  ;  such  artifacts,  also  atrophying  capil- 
laries, have  been  described  as  "vasoformative  cells." 

No.  43. — Colored  blood- cells  of  mati. — Carefully  cleanse  a  slide  and 
a  small  cover-glass  (finally  with  alcohol).  With  a  needle  cleansed 
shortly  before  by  heating  prick  the  finger-tip  at  one  side ;  lightly 
touch  the  first  drop  of  blood  that  escapes  with  the  cover-glass  and  at 
once  put  it  on  a  small  drop  of  0.75  per  cent,  salt  solution  previously 
placed  on  the  slide.  With  the  high  power  many  colored  cells  adhering 
to  one  another  by  their  broad  surfaces,  forming  the  so-called  rouleaux 
(Fig.  80),  can  be  seen,  as  well  as  isolated  colored  and  colorless  blood- 
cells.  The  distortion  of  many  of  the  colored  cells  is  due  to  evapora- 
tion, in  consequence  of  which  they  are  beset  with  minute  spines,  are 
crenated.  If  a  drop  of  water  be  placed  at  the  edge  of  the  cover-glass, 
the  cells  soon  become  decolorized  and  the  water  acquires  a  yellowish 
tinge  ;  at  the  same  time  the  cells  become  spherical,  have  the  appearance 
of  pale  circles,  "shadows,"  and  finally  disappear.  In  studying  this 
process  of  decoloration  the  student  is  advised  to  concentrate  his  atten- 
tion upon  a  single  cell. 

No.  44. — Permanent  preparation  of  colored  blood- cells. — By  means 
of  a  sable  pencil  spread  living  blood,  fresh  from  the  finger,  in  the  thin- 
nest possible  film  on  a  carefully  cleaned  slide  and  let  it  dry  in  the  air. 
Cover  the  dry  preparation  with  a  dry  cover-glass  and  seal  the  edges  with 
cement  (p.  50).  Among  many  misshapen  forms  a  few  blood-cells,  well- 
preserved  in  form  and  size,  may  be  found. 

No.  45. — Permanent  preparatio7is  of  colored  and  colorless  blood-cells 
are  made  by  Ehrlich's  dry  method.  This  method  accurately  carried  out, 
after  some  practice,  yields  good  results,  but  with  unskilful  manipulation 
many  caricatures  arise  and  mislead  the  inexperienced.  The  employment 
of  this  method  for  purposes  of  investigation  and  discovery  requires 
great  skill  and  great  caution  in  judgment. 


THE    CIRCULATORY    SYSTEM.  155 

Preliminary  ma7iipulations. — For  each  preparation  two  tliin  cover- 
glasses  are  required,  they  should  not  be  over  o.  i  mm.  thick  and  should 
be  cleaned  by  placing  them  for  a  few  minutes  in  dilute  hydrochloric  acid, 
then  in  distilled  \vater,  and  finally  in  alcohol.  It  is  best  to  take  cover- 
glasses  that  have  never  been  used.  Prepare  a  mixture  of  equal  parts  of 
absolute  alcohol  and  ether  (about  5  c.c.  of  each).  Cleanse  the  tip  of  the 
finger  first  with  soap  and  water,  then  with  a  tuft  of  clean  cotton- 
wool moistened  with  the  alcohol-ether  mixture.  With  a  clean  needle 
(not  previously  used  for  anatomic  purposes)  prick  the  pad  of  the  finger, 
made  slightly  hyperemic  by  compression  ;  take  up  a  cover-glass  with 
the  forceps  (not  with  the  fingers),  press  it  lightly  upon  the  escaping  drop 
of  blood  and  place  it  on  the  second  cover- glass,  with  one  edge  project- 
ing slightly.  The  drop  of  blood  will  spread  out  in  a  thin  film  between 
the  two  glasses,  which  are  then  slipped  apart  by  means  of  two  forceps. 
By  this  manipulation  the  influence  of  the  insensible  perspiration  on  the 
blood-cells  is  prevented,  which  otherwise  would  shrink  or  lose  their 
hemoglobin. 

Exposed  to  the  air  the  blood  on  the  cover-glasses  dries  in  a  few 
minutes  ;  they  are  then  to  be  placed  in  the  alcohol-ether  mixture  for 
fixation.  In  from  one-quarter  to  two  hours  they  should  be  removed, 
again  dried  in  the  air,  when  they  are  ready  for  further  treatment,  which 
may  be  applied  immediately  or  later,  since  the  fixed  preparations  can  be 
preserved  for  a  long  time. 

Fiu'ther  treatment,  {a)  Oxyphile  [eosinophile,  «)  granules. — Place  the 
cover-glass  preparations  for  twenty-four  hours  in  about  4  c.c.  of  distilled 
water  to  which  about  10  drops  of  eosin  solution  have  been  added.  Rinse 
one  minute  in  distilled  water  and  stain  for  from  one  to  five  minutes  in  a 
watch-glass  with  Hansen's  hematoxylin  (p.  38).  Transfer  to  distilled 
water  ;  remove  in  five  minutes  and  let  the  preparations  dry  in  air  under 
a  bell-glass.  Mount  the  dry  preparation,  without  further  treatment,  in  a 
drop  of  xylol-balsam.  The  colored  blood-cells  and  the  oxyphile  gran- 
ules of  the  colorless  blood-cells  are  stained  bright  red  ;  the  nuclei  are 
blue.  The  oxyphile  granules  occur  sparingly  (2  to  4  per  cent.)  in  the 
leucocytes  of  normal  blood,  of  lymph,  and  of  the  tissues.  They  are 
numerous  in  the  bone-marrow  of  the  rabbit.  A  magnification  of  400 
diameters  is  sufficient  to  find  them. 

{b)  Basophile {mast-cell)  grajiules. — Stain  the  dry  cover-glass  prepara- 
tion after  the  method  given  in  No.  7,  p.  lOi,  dry,  and  mount  in  balsam. 
These  granules  are  rare  in  normal  blood  (0.5  per  cent,  at  most). 

{c)  Nentrophile  (s-)  granules. — (i)  Dissolve  i  gm.  of  orange-yellow 
extra  in  50  c.c.  of  distilled  water  ;  (2)  i  gm.  of  acid-fuchsin  extra  in 
50  c.c.  of  distilled  water ;  (3)  i  gm.  of  crystalline  methyl-green  in 
50  c.c.  of  distilled  water,  and  let  the  three  solutions  settle.  Then  mix 
II  c.c.  of  solution  (i)  with  10  c.c.  of  solution  (2)  and  add  20  c.c.  of 
distilled  water  and  10  c.c.  of  absolute  alcohol;  to  this  mixture  add  a 
mixture  of  13  c.c.  of  solution  (3),  10  c.c.  of  distilled  water,  and  3  c.c.  of 
absolute  alcohol.  The  whole  is  then  allowed  to  stand  for  one  or  two 
weeks.      In    this    "  triacid   solution"    the    dry    cover-glass    preparation 


I  56  HISTOLOGY. 

should  be  placed  for  fifteen  minutes,  then  washed,  dried,  and  mounted 
in  balsam.  The  neutrophile  granules,  which  are  found  in  leucocytes 
with  lobulated  nuclei  of  normal  and  other  blood,  are  of  a  violet  color 
and  are  easily  seen  with  the  usual  dry  high-power  lenses  ;  the  oxyphile 
granules  and  the  colored  blood-cells  are  of  a  yellow-brown  to  chocolate - 
brown  color,  the  nuclei  a  bright  blue-green,  though  their  outlines  are  not 
so  distinct  as  in  the  hematoxylin  preparations. 

No.  46. — Blood-platelets. — Mix  about  5  drops  of  an  aqueous  solu- 
tion of  methyl-violet  (p.  26)  with  about  5  c.c.  of  salt  solution  (p.  20). 
Filter  the  mixture  and  place  a  drop  of  it  on  the  tip  of  the  finger  ;  prick 
the  finger  through  the  drop  ;  the  escaping  blood  mixes  with  the  methyl- 
violet  ;  take  up  a  drop  with  the  cover-glass  and  examine  with  the  high 
power.  The  platelets  are  stained  an  intense  blue  of  a  peculiar  luster, 
are  disk-shaped  (Fig.  80),  and  should  not  be  confused  with  the  white 
blood-cells  likewise  stained  blue.  They  are  numerically  variable  elements, 
occurring  in  large  numbers  in  the  blood  of  one  individual,  while  in  the 
blood  of  another  they  are  only  to  be  found  singly  here  and  there.  Care 
must  be  taken  not  to  confuse  them  with  foreign  particles,  which  may 
occur  even  in  the  filtered  staining  solution. 

No.  47. — Colored  blood-cells  of  the  frog. — Prepare  the  slide  and 
treat  the  blood,  taken  from  the  recently  killed  animal,  after  No.  43. 

No.  48. — For  forensic  purposes. — Since  it  is  usually  dried  blood  that 
is  to  be  examined,  dissolve  small  particles  of  dried  blood  in  35  per  cent, 
potash  solution  on  a  slide  ;  blood-stained  pieces  of  linen  may  be  teased 
in  a  drop  of  the  same  solution.  Although  the  colored  blood-cells  of 
native  mammalian  animals  are  smaller  than  those  of  man,  it  is  never- 
theless impossible  from  the  size  of  the  blood-cell  to  determine  its  source. 
On  the  other  hand,  it  is  easy  to  distinguish  the  disk-shaped  cells  of 
mammals  from  the  oval  elements  of  other  vertebrates. 

No.  49. — Colorless  blood-cells  {leucocytes^  m  motioji. — Prelimmary 
maniptdations :  Carefully  cleanse  a  slide  and  cover-glass  with  alcohol. 
Kill  a  frog,  grasp  it  by  its  hind  legs,  dry  its  back  somewhat  with  a  cloth, 
and  with  fine  scissors  make  an  incision  i  cm.  long  parallel  to  and  close 
beside  the  vertebral  column.  Introduce  a  capillary  pipet  into  the  wound 
(with  the  tip  directed  forward)  and  suck  the  tip  full.  A  small  drop  is 
sufficient ;  blow  it  on  to  the  slide,  cover  it  quickly,  and  seal  the  edges 
with  melted  paraffin  (p.  53).  Such  a  preparation  shows  colored  and 
colorless  blood-cells  ;  at  first  the  nuclei  of  the  former  are  indistinct. 
The  nuclei  of  living  colorless  blood-cells  are  in  general  invisible.  For 
the  study  of  ameboid  movement  select  leucocytes  the  protoplasm  of 
which  is  partly  granular  and  which  are  not  spherical.  The  movements 
are  slow  ;  of  this  one  can  best  convince  one's  self  by  studying  a  single 
leucocyte  and  making  sketches  of  it  at  intervals  of  from  one  to  two 
minutes.      Study  with  the  high  power  (Fig.  6). 

No.  50. — Blood-crystals. — [a)  Hemin  crystals  are  easily  obtained. 
Cut  a  small  strip  about   3  mm.  wide  from  a   piece  of  linen  previously 


THE    CIRCULATORY    SYSTEM.  I  57 

saturated  with  blood  and  dried  and  place  it  with  a  pinhead-sized  crystal 
of  common  salt  on  a  clean  slide  ;  add  a  large  drop  of  glacial  acetic  acid 
and  with  a  glass  rod  stir  the  linen  and  salt  for  about  one  minute  or 
until  the  acid  acquires  a  brownish  tinge.  Then  heat  the  slide  over  the 
flame  until  the  acetic  acid  boils.  Quickly  remove  the  linen  and  examine 
the  dry  brown  places  on  the  slide  with  the  high  power  (from  240  diame- 
ters up).  Occasionally  the  brown  crystals  can  be  seen  without  the  cover- 
glass  and  without  a  mounting  medium,  lying  next  to  numerous  fragments 
of  white  salt-crystals  (Fig.  82,  i).  For  preservation  add  a  large  drop  of 
balsam  and  apply  a  cover-glass.  The  hemin  crystals  differ  greatly  in 
form  and  size.  Well-developed  crystals  lying  singly  or  crosswise  over  one 
another,  or  arranged  in  stellate  groups,  whetstone  forms  and  minute  par- 
ticles that  scarcely  exhibit  crystallization  are  obtained  from  the  same  drop 
of  blood.  The  demonstration  of  the  hemin  crystals  is  of  great  import- 
ance in  a  forensic  respect.  While  it  is  easy  to  obtain  the  crystals  in 
large  stains  on  wearing  apparel,  it  is  difficult  when  the  stains  are  small, 
especially  on  rusty  iron,  to  prov^e  that  they  are  from  blood.  The  instru- 
ments and  reagents  employed  in  such  investigations  must  be  absolutely 
free  from  contamination. 

{b)  Hematoidin  crystals  are  obtained  by  teasing  old  blood  extravasa- 
tions ;  they  can  be  recognized  macroscopically  by  their  reddish-brown 
color,  for  example,  in  the  corpus  luteum,  in  cerebral  hemorrhages 
(Fig.  82,  3)-  . 

(<r)  Hemoglobin  crystals  are  obtained  by  transferring  5  c.c.  of  the 
blood  of  a  dog  to  a  test-tube,  adding  a  couple  of  drops  of  ether,  and 
shaking  vigorously  until  the  blood  becomes  lake-colored.  Then  spread 
a  few  drops  on  a  slide  and  let  the  preparation  dry  in  the  cold.  When 
crystallization  has  occurred  add  a  drop  of  glycerol  and  apply  a  cover- 
glass.  The  large  crystals  often  exhibit  a  tendency  to  cleave  lengthwise 
(Fig.  82,  4  ^). 

No.  51. — Lymph-vessels. — For  the  study  of  the  walls  of  the  larger 
lymph-vessels,  select  the  vessels  opening  into  the  inguinal  glands,  that 
are  large  enough  to  be  taken  out  with  forceps  and  scalpel.  Prepare  like 
the  large  blood-vessels,  No.  37,  or  after  No.  39  b. 

No.  52. — For  the  exhibition  of  the  more  delicate  lymph-vessels,  of 
their  course  and  their  distribution,  the  method  of  interstitial  injection  is 
often  employed.  The  needle  of  a  hypodermic  syringe  filled  with  Berlin 
blue  is  thrust  haphazard  into  the  tissue  ;  this  is  a  crude  method,  the 
results  of  which  are  of  v^ery  doubtful  value.  Even  though  here  and 
there  actual  lymph-vessels  may  thus  be  filled,  in  most  cases  the  injec- 
tion-mass is  simply  driv^en  forcibh'  into  the  interfascicular  clefts  of  the 
connective  tissue.  The  value  of  any  opinion  with  regard  to  "  radicles 
of  lymph-vessels  "  and  to  "  lymph-spaces  "  thus  exhibited  is  self-evident. 

No.  53. — Lymph-glands. — For  a  general  view  the  mesenteric  glands 
of  kittens  are  suitable.  For  fixation  and  hardening  place  them  in  30  c.c. 
of  absolute  alcohol  ;  in  three  days  thin  sections  can  be  readily  made 
and   should    be  taken   so  that    the\-  pass  through  the  hilus,   which  is 


158  HISTOLOGY. 

easily  recognized  macroscopically  by  an  external  depression.  Longi- 
tudinal sections  passing  through  the  poles  of  the  glands  are  best, 
though  transverse  sections  are  also  useful.  Stain  six  or  eight  sections 
in  Hansen's  hematoxylin  for  from  two  to  three  minutes,  then  in  eosin 
for  one  minute  (No.  3  i^b),  p.  39),  transfer  them  to  a  test-tube  half 
filled  with  distilled  water  and  shake  them  for  from  three  to  five  minutes. 
Pour  the  shaken  sections  into  a  flat  dish  ;  the  cortex  and  medulla  can  be 
macroscopically  distinguished  by  the  uniformly  blue  color  of  the  former 
and  the  variegated  appearance  of  the  latter.  Mount  in  xylol-balsam. 
The  trabeculae  are  but  slightly  developed.  The  fragments  of  adipose 
tissue  adhering  to  the  glands  must  not  be  taken  for  reticular  tissue. 
High  magnification  is  of  no  advantage,  the  sharp  outlines  disappear  and 
the  picture  loses  in  distinctness. 

No.  54. — Lymph-glands  of  mature  ajtim ah  and  of -man  are  difficult 
to  understand,  because  the  entire  cortex  is  transformed  into  a  con- 
tinuous mass  irregularly  sprinkled  with  germinal  centers.  Still,  thin 
sections  of  small  glands  fixed  in  Zenker's  fluid  (p.  33)  and  hardened  in 
gradually  strengthened  alcohol  (p.  35),  stained  after  the  method  of  van 
Gieson  (p.  43),  give  satisfactory  pictures  (Fig.  84).  The  lymph  sinuyes 
cannot  be  brought  distinctly  to  view  by  shaking  the  sections  and  the 
germinal  centers  are  apt  to  fall  out  and  leave  round  spaces  macroscopi- 
cally recognizable. 

No.  55. — The  mesenteric  follicles  of  the  ox  are  well  adapted  for  the 
representation  of  the  network  of  medullary  cords  and  trabeadcE.  Place 
pieces  2  cm.  long  in  200  c.c.  of  concentrated  aqueous  picric-acid  solu- 
tion and  after  twenty-four  hours,  with  a  sharp  knife  moistened  with 
water,  try  to  cut  thin  sections.  This  is  not  so  easily  done  as  after 
alcohol  fixation,  but  slightly  thicker  sections  can  be  used.  Place  the 
sections  for  one  hour  in  100  c.c. of  distilled  water,  which  must  be  changed 
frequently,  stain  with  Hansen's  hematoxylin  and  with  eosin  (No.  3  (^),  p. 
39),  and  shake  them  (see  No.  53).  Mount  in  xylol-balsam  (p.  50).  The 
trabeculae  are  red,  the  medullary  cords  blue  ;  with  low  magnification  the 
picture  is  like  Fig.  86  ;  with  high  magnification  the  reticular  connective 
tissue  of  the  lymph  sinuses  can  be  seen  ;  the  majority  of  the  leucocytes 
occupying  the  meshes  become  loosened  by  the  treatment  with  picric  acid 
and  are  lost  in  the  shaking  (Fig.  87). 

No.  56. — Elements  of  the  spleen. — Make  an  incision  through  a  fresh 
spleen ;  with  a  scalpel  obliquely  applied  scrape  the  cut  surface  and 
examine  a  little  of  the  red  mass  adhering  to  the  blade  in  a  drop  of  salt 
solution.  Use  the  high  power.  Often,  especially  in  animals,  only 
colored  and  colorless  blood  corpuscles  are  found  ;  some  of  the  latter 
contain  minute  granules.  In  human  spleens,  in  addition  to  the  numer- 
ous colored  blood-cells  altered  in  form,  epithelial  cells  of  the  lymph 
sinuses  are  always  found  ;  the  latter  were  formerly  called  "  spleen-fibers  " 
(Fig.  91,2,  3).  In  many  human  spleens  multinucleated  cells  and  cells 
containing  erythrocytes  are  often  sought  in  vain  (Fig.  91,  4). 


THE    SKELETAL    SYSTEM.  I  59 

No.  57. —  TJic  Spleen. — Without  cutting  it,  fix  the  entire  spleen  in 
Miiller's  fluid  (p.  33),  using  one  Hter  for  a  human,  200  to  300  c.c.  for  a 
cat's  spleen.  After  two  weeks  for  the  cat's,  five  weeks  for  the  human 
spleen,  wash  for  from  one  to  two  hours  in  running  water,  cut  out  pieces 
2  cm.  square  and  harden  them  in  60  c.c.  of  gradually  strengthened  alco- 
hols (p.  35).  The  spleen  nodules  can  be  seen  on  the  cut  surface  with 
the  unaided  eye.  Sections  not  too  thin  are  to  be  stained  in  Hansen's 
hematoxylin  and  mounted  in  balsam.  If  it  is  desired  to  differentiate  the 
trabeculae,  after  staining  in  hematoxylin  place  the  sections  for  a  half 
minute  in  eosin  *  (No.  3  (^),  p.  39).  In  successful  preparations  the  pulp 
cords  and  the  spleen  nodules  are  blue,  the  trabecule  rosy,  the  vessels  dis- 
tended with  blood  corpuscles  brown.  The  sections  are  most  satisfactory 
when  examined  with  a  very  low  power  (Fig.  90) ;  with  the  high  power 
the  outlines  are  often  indistinct.  Fixation  in  Zenker's  fluid  (p.  33)  is 
recommended  for  thin  sections,  with  staining  after  van  Gieson  (p.  43). 

No.  58. —  Reticular  coimective  tissue  of  the  spleen. — Shake  a  thin 
section  fixed  and  stained  according  to  No.  57  for  about  five  minutes  in  a 
test-tube  half  filled  with  distilled  water.  Mount  in  glycerol.  The  leu- 
cocytes are  difficult  to  dislodge  ;  the  narrow-meshed  network  can  be  seen 
only  at  the  edges  of  the  preparation  (Fig.  92). 

No.  59. — Blood-vessels  of  the  spleen  z.x&  incidentally  exhibited  by  in- 
jecting the  stomach  and  intestine  (compare  with  No.  1 16). 

No.  60. — Nerves  of  the  spleen. — For  this  purpose  the  spleen  of  the 
mouse  is  best  suited.  Halve  it  and  apply  Golgi's  method  for  the  demon- 
stration of  the  elements  of  the  nervous  system  (p.  45).  It  is  sometimes 
sufficient  to  place  the  object  in  the  osmio-bichromate  mixture  (in  a  warm 
oven)  for  three  days  and  for  the  same  length  of  time  in  the  silver  solu- 
tion ;  often  a  repetition  of  the  whole  process  once  or  twice  yields  good 
results. 

II.   ORGANS   OF  THE   SKELETAL  SYSTEM. 

The  skeletal  system  mainly  consists  of  a  large  number  of  firm 
bodies,  the  bones,  which  are  joined  together  by  special  structures  and 
in  their  entirety  form  the  skeleton. 

In  the  embryo  the  greater  part  of  the  skeleton  consists  of  cartilage, 
which  in  the  course  of  development  is  supplanted  by  bone  and  with  the 
exception  of  a  few  remnants  disappears  ;  such  remnants  are  the  costal 
cartilages  and  the  cartilages  of  the  joints,  which  cover  the  articular  sur- 
faces of  many  bones.  Skeletal  cartilages  are  also  found  in  the  respira- 
tory passages  and  in  the  organs  of  special  sense. 

*  Longer  staining  makes  the  erythrocytes  bright  red,  the  trabeculae  dark  red,  and  the 
easy  distinction  between  them  is  lost. 


i6o 


HISTOLOGY. 


The  Bones. 
On  sawing  through  a  fresh  bone  at  once  it  will  be  seen  that  its 
texture  is  not  everywhere  alike,  but  that  the  osseous  tissue  appears  in 
two  forms  :  the  one,  a  very  dense,  firm,  apparently  structureless  substance, 
constitutes  the  principal  portion  of  the  periphery  and  is  termed  compact 
bone  (substantia  compacta)  ;  the  other,  toward  the  axial  cavity,  appears 
as  an  irregular  reticulum  of  thin  osseous  lamells  and  slender  trabeculae, 
and  is  called  spongy  bone  (substantia  spongiosa).  The  interstices  of  the 
spongy  bone,  as  well  as  the  central  marrow-cavity,  are  filled  with  a  soft 
mass,  the  bone-marrow  ;  the  surface  of  the  bone  is  enveloped  in  a  fibrous 


Haversian  canals. 


f Ground  substance. 


•^    lit  —       Periosteum. 


Fat-drops. 


Fig.  95. — From  a  Longitudinal  Section  of  a  Human  Metacarpus.  X  30.  Fat-drops  are  seen  in 
the  haversian  canals.  At  x  haversian  canals  open  on  the  outer,  and  at  xx  on  the  inner  surface  of  the 
bone.     Technic  No.  63. 

membrane,  the  periosteum.  The  proportion  between  the  compact  and 
the  spongy  substance  is  somewhat  different  in  the  sliort  bones,  which 
consist  chiefly  of  the  latter,  the  compact  substance  being  confined  to  a 
narrow  zone  at  the  periphery.  Flat  bones  have  a  sometimes  thicker, 
sometimes  thinner  cortex  of  compact  substance,  while  the  interior  is 
filled  with  spongy  substance.  In  the  epiphyses  of  the  long  bones,  as  in 
the  short  bones,  the  spongy  substance  preponderates. 

The  spongy  substance  consists  entirely  of  osseous  tissue  (p.  98)  ;  the 
compact  substance,  on  the  other  hand,  contains  besides  the  bone  canaliculi 
and  lacunae  a  second  system  of  larger  canals,  from  22  to  no  //  wide, 
which  divide  dichotomously  and  form  a  wide-meshed  network.      These 


THE    SKELETAL    SYSTEM. 


l6l 


canals  contain  the  blood-vessels  and  are  named  haversian  canals.  In 
the  long  bones,  in  the  ribs,  in  the  clavicle,  and  in  the  inferior  maxilla 
their  course  is  parallel  to  the  long  axis  of  the  bone  ;  in  short  bones  they 
run  mainly  in  one  direction,  for  example,  vertically  in  the  vertebrae  ; 
in  the  flat  bones  their  course  is  parallel  to  the  surface,  not  infrequently 
in  lines  that  radiate  from  a  point,  as  in  the  tuberosity  of  the  parietal 
bone.  The  haversian  canals  open  on  the  outer  surface  of  the  bone 
(Fig.  95,  x),  as  well  as  on  the  inner  surface  (Fig.  95,  xx)  directed  toward 
the  substantia  spongiosa. 

The  ground-substance  of  compact  bone  is  arranged  in  lamellse,  that 
is,  the  osseous  fibrillae  (p.  98)  are  joined  in  bundles  and  these  placed  side 
by  side  form  thin  plates  or  lamella?.  According  to  the  disposition  of 
these  plates  three  lamellar  systems  can  be  distinguished  :  an  annular 


Periosteum. 

Outer  ground  lamellas. 


-   Haversian  canals. 


Haversian  lamellae. 

Interstitial  lamellse. 
Inner  ground  lamellae. 

Marrow. 


Fig.  96.- 


-From  a  Cross-section  of  a  Metacarp  of  Man.    X  50.    The  haversian  canals  contain  a  little 
marrow  (fat-cells).     Resorption  line  at /;.     Technic  No.  63. 


system  encircling  the  haversian  canals,  which  in  cross-section  exhibits 
from  eight  to  fifteen  lamellae  concentrically  arranged  around  an  haversian 
canal  ;  these  lamellae  are  called  haversian  or  special  lanielhv  (Fig.  96). 
Transverse  sections  show  that  the  haversian  systems  are  in  contact  in 
portions  of  their  circumference,  elsewhere  are  kept  apart  by  strata  of 
osseous  lamella;  running  in  a  different  direction.  These  more  irregularly 
disposed  lamellae  between  the  haversian  systems  are  named  intercalated 
or  interstitial  lamella; ;  they  are  connected  with  the  third,  superficial 
lamellar  system,  the  general  or  ground  lamella;,  in  which  the  osseous 
strata  encircle  the  outer  surface  of  the  bone  and  are  called  onter  ground 
lamella; ;  occasionally  similar  circular  lamellae  are  found  on  the  inner 
free  surface  and  are  named  inner  ground  lamella;.  The  general  lamella; 
contain  an  extremely  variable  number  of  canals  for  vessels,  which  unlike 
the  haversian  canals  are  not  the  centers  of  annular  systems  of  lamellae  ; 
II 


1 62  HISTOLOGY. 

they  are  called  Volkmann's  canals  and  the  contained  vessels,  the  "per- 
forating vessels."  The  latter  freely  connect  with  the  vessels  of  the 
haversian  canals;  the  transition  of  Volkmann's  canals  into  the  haversian 
canals  is  a  very  gradual  one. 

The  bone  lacunae  in  the  compact  substance  have  quite  definite 
positions.  In  the  haversian  lamellar  systems  their  long  axis  is  parallel 
to  the  long  axis  of  the  haversian  canals  and  they  are  bent  in  the  direc- 
tion of  the  surface,  so  that  cut  transversely  they  appear  concentrically 
curved  to  the  cross-section  of  the  haversian  canal.  In  the  interstitial 
lamellae  the  lacunae  are  placed  irregularly,  in  the  ground  lamellae  so  that 
their  surfaces  run  parallel  to  the  surfaces  of  the  lamellae.  The  bone 
canaliculi  open  into  the  haversian  canals  and  on  the  free  outer  and  inner 
surfaces  of  the  bone. 

The  bone  marrow  occupies  the  axial  cavity  of  the  tubular  bones, 
fills  the  interstices  of  the  spongy  substance,  and  is  also  found  in  the 


^j. ^  Hematoblasts. 

\.j-—     Colored  blood-cell. 
Megakarvocvte. 


Fig.  97. — Elements  of  Human  Bone  Marrow.    X  600.    1-5.  Various  forms  of  marrow  cells. 
6.  Eosinophile  cell.     Technic  No.  64  b. 

larger  haversian  canals.  It  is  of  a  red  or  a  yellow  color  and  therefore  two 
varieties  are  distinguished,  the  red  marroiv  and  the  yellow  marrow.  The 
red  marrow  is  found  in  the  flat  bones,  in  the  vertebrae,  in  the  base  of  the 
skull,  in  the  sternum,  in  the  ribs,  and  in  all  young  bones  (also  in  the 
long  bones  of  small  animals)  ;  the  yellow  marrow  occurs  in  the  short 
and  long  bones  of  the  extremities.  In  old  and  in  sick  persons  the 
marrow  is  mucoid  and  reddish-yellow  and  is  then  called  gelatinous  bone- 
marrow  ;  it  is  characterized  simply  by  its  poverty  in  fat. 

The  elements  of  red  marroiv  are  connective  tissue,  marrow  cells, 
giant  cells,  and  hematoblasts.  The  scanty  connective  tissue  consists  of 
bundles  of  fibrillse,  connective-tissue  cells,  and  fat-cells.  In  the  large 
marrow  cavities  the  bundles  of  fibrillae  are  denser  and  form  alining  mem- 
brane, the  endostenm,  while  in  the  marrow  spaces  of  the  spongy  sub- 
stance they  are  almost  entirely  wanting.  Elastic  elements  are  absent. 
The  marrow  cells  are  leucocytes  and  predominantly  uninuclear  neutro- 
phile  (so-called  myelocytes)   and  polymorphous-nuclear  varieties  (Fig. 


THE    SKELETAL    SYSTEM. 


163 


81  d,c);  also  eosinophile  leucocytes,  mast-cells,  and,  in  considerably 
lesser  quantity,  nongranular  uninuclear  cells.  The  giant  cells  are  huge, 
extremely  irregularly  shaped  structures,  of  which  two  varieties  are  dis- 
tinguished :  (a)  megakaryocytes  (Fig.  97),  cells  with  one  huge  nucleus, 
varying  greatly  in  shape  ;  it  is  round,  or  lobed,  or  flat  and  ring-like 
(Fig.  109,  2  r)  or  it  forms  a  network  ;  {b)  ostoclasts  (p.  177),  cells  contain- 
ing several  small  nuclei  (Fig.  104  and  108)  ;  they  invariably  lie  in  the 
neighborhood  of  the  bone,  or  of  the  cartilage,  while  the  megakaryocytes 
lie  in  the  interior  of  the  marrow. 


Hematoblast 


Eosinophile  cell. 


.Marrow  cell. 


-^^,   ,       \ai>  y*^  Marrow 


cell. 


Fat  space. 


Connective- 
tissue  reticu- 
lum. 


Hematoblast.        Eosinophile  cell. 

Fig.  98.— Section  of  the  Bone  Marrow  of  a  Rabbit,  showing  the  Delicate  Connective-tissue 
Reticulum  Containing  the  Different  Elements  of  the  Marrow.     X  400.    (Schaper.) 

Many  giant  cells  are  structural  anomalies  related  to  leucocytes,  being 
enlarged  and  modified  forms  of  the  latter ;  the  ostoclasts,  according  to  recent 
investigations,  are  said  to  originate  in  the  walls  of  the  blood  capillaries,  by 
proliferation  of  the  protoplasm  and  multiplication  of  the  nuclei  of  the  epi- 
thelial cells  and  subsequent  constriction  from  the  maternal  basis.  By  con- 
striction of  the  nucleus  into  several  parts  a  uninuclear  giant  cell  may 
become  a  multinuclear  cell  (Fig.  109,  3  r)  ;  or  with  the  nuclear  particles  corre- 
sponding portions  of  the  protoplasm  may  be  separated  by  constriction,  result- 
ing in  uninuclear  cells  (cf.  budding,  p.  72).  The  supposition  that  these 
processes  of  division  are  the  phenomena  of  a  reversed  series  of  processes, 
the  merging  of  several  cells  into  one,  has  very  little  probability,  since  the 
process  of  budding  has  been  observed  in  living  cells.  Trophospongium 
canals  have  been  observed  in  the  giant  cells  (p.  64). 


164  HISTOLOGY. 

The  lieniatoblasts  are  nucleated  cells  with  yellow  colored  proto- 
plasm, resembling  that  of  the  erythrocytes.  They  are  the  mother  cells 
of  the  erythroc}-tes  (Fig.  97  and  98).  Yellowish  pigment  corpuscles 
occurring  in  various  cells  are  regarded  as  remains  of  degenerated  red 
blood-cells. 

The  yellow  marrow  consists  of  much  fat  and  of  connective  tissue. 
Marrow  cells  and  hematoblasts  are  found  only  in  the  yellow  marrow  of 
the  head  of  the  humerus  and  of  the  femur. 

The  periostewn  is  a  compact  membrane  consisting  of  connective - 
tissue  fibers,  in  which  two  layers  can  be  distinguished.  The  outer  layer, 
the   "  adventitia,"   is  characterized   by  its  richness  in   blood-vessels  and 


Outer  ground 
lamellae. 


Volkmann's  canals. 


.  Haversian  lamellae. 

Sharpey's  fibers.  ^- tt— -:=-^-^^^^_-  „    -  -     '^;   '   ^  °  =   "i   /  ?^^^^- Haversian  canal. 


■  Interstitial  lamellae. 


.f 


Fig.  99. — From  A  Cross-section  OF  THE  Femur  OF  Adult  Man.    X8o.    Technic  N0.62.    The  lamellae 
can  be  recognized  by  the  position  of  the  lacunas. 

establishes  the  connection  with  adjacent  structures,  tendons,  fasciae,  etc.  ; 
the  inner  layer,  the  "  fibro-elastica,"  is  poor  in  blood-vessels,  but  is  very 
rich  (particularly  at  the  insertions  of  fascise  and  tendons)  in  elastic  fibers 
running  parallel  with  the  long  axis  of  the  bone  and  in  spheric  or  spin- 
dle-shaped connective-tissue  cells.  Here  and  there  on  the  inner  surface 
a  layer  of  cubical  cells  '^'  is  found,  that  are  of  importance  in  the  devel- 
opment of  the  bone.  The  periosteum  is  sometimes  firmly,  sometimes 
loosely  attached  to  the  bone  ;  the  attachment  is  effected  by  the  blood- 
vessels passing  to  and  from  the  bone  and  by  Sharpey's  fibers  (p.  98, 
remark  tj,  which  pierce  the  outer  ground  and  the  adjacent  interstitial 
lamellae  and  extend  in  all  directions  (Fig.  99).  In  the  tubular  bones 
elastic  elements  of  the  fibro-elastica  of  the  periosteum  penetrate  the 
bone  in  company  with  many  Sharpey's  fibers  and  without  regard  to  the 

*The  vitality  of  the  cells  of  the  fibro-elastica  is  very  great.  The  periosteum  of  a  corpse 
kept  at  15°  C,  which  is  transplanted  168  hours  after  the  death  of  the  organism  is  said  to  be 
still  capable  of  producing  cartilage  and  osseous  tissue. 


THE    SKELETAL    SYSTEM.  1 65 

lamellar  structure  of  the  bone  run  in  the  more  superficial  strata.  There 
are  also  elastic  fibers  that  penetrate  independently  of  Sharpey's  fibers. 
In  the  bones  of  the  vertex  of  the  skull  elastic  elements  are  wanting. 

The  blood-vcssiis  of  the  bone,  the  marrow,  and  the  periosteum  are 
in  the  closest  connection  with  one  another,  and  also  with  surrounding- 
structures.  Small  branches  (not  capillaries)  of  the  numerous  arterial 
and  venous  vessels  of  the  periosteum  everywhere  enter  the  haversian  and 
Volkmann's  canals  and  on  the  inner  surface  of  the  bone  are  in  communi- 
cation with  the  blood-vessels  of  the  marrow.  The  latter  is  supplied  by 
the  nutrient  artery,  which  on  its  way  through  the  compact  substance 
gives  off  branches  to  the  same  and  in  the  marrow  breaks  up  into  a  rich 
vascular  network.  The  capillaries  of  the  marrow  form  wide,  very 
thin-walled,*  valveless  veins  ;  of  the  larger,  likewise  valveless,  veins  one 
accompanies  the  nutrient  artery,  while  the  others  make  numerous  con- 
nections with  the  veins  of  the  compact  substance.  True  lymph-vessels 
occur  only  in  the  most  superficial  layers  of  the  periosteum. 

The  nerves  are  numerous  and  consist  partly  of  medullated,  partly 
of  nonmedullated  fibers.  Thej'  enter  the  haversian  canals  and  the  bone 
marrow,  also  the  periosteum,  where  occasionalh'  they  terminate  in  lamel- 
lar corpuscles. 

The  Articulations  of  Boxes. 

Two  forms  of  articulation  are  recognized  :  synarthroses,  joints  char- 
acterized by  immobility  ;  diarthroses,  ]om\.s  in  which  the  bones  are  mov- 
able, one  upon  the  other. 

In  synarthroses  the  bones  are  joined  either  by  ligaments,  the  union 
constituting  a  syndesmosis  ;  or  by  the  intervention  of  cartilage,  forming  a 
syncho7tdrosis. 

The  ligaments  are  ^aiXtXy  Jibrons  bands,  possessing  a  structure  like 
that  of  tendon,  partly  elastic  bands.  The  latter  are  distinguished  by  the 
possession  of  numerous  robust  elastic  fibers,  which  are  never  arranged 
in  bundles  or  lamellae,  but  are  alwa}'s  separated  by  loose  connective  tis- 
sue [cf.  Fig.  35  C).  The  ligamentum  nuchse,  the  ligamenta  subflava, 
and  the  ligamentum  stylohyoideum  are  elastic  ligaments. 

The  sutures  also  belong  to  the  syndesmoses  ;  they  are  short  fibrous 
ligaments  that  extend  from  one  serrated  osseous  edge  to  the  other. 

The  cartilage  in  synchondroses  is  rarely  only  of  the  h}-aline  variety, 
but  usually  is  in  part  fibro-cartilage  and  (especially  at  the  borders  in  con- 
tact with  the  bone)  in  part  hyaline,  in  which  the  cell-capsules  are  fre- 
quently calcified. 

*  These  delicate  walls  were  formerly  overlooked,  whence  arose  the  teaching  that  blood- 
spaces  without  walls  exist  in  bone  marrow. 


1 66 


HISTOLOGY. 


The  intervertebral  ligaments,  which  likewise  belong  to  the  synchon- 
droses, possess  in  their  center  a  soft,  gelatinous  substance,  the  nucleus 
pulposus,  that  contains  large  groups  of  cartilage  cells  ;  it  is  the  remains 
of  the  notochord,  the  embryonic  precursor  of  the  vertebral  column.  At 
the  periphery  of  the  intervertebral  ligaments  there  is  a  narrow  tendinous 
zone. 

In  diartliroses  the  parts  entering  into  a  joint  are  the  articular  ends 
of  the  bones,  the  capsular  ligament,  the  marginal  fibro-cartilages  {labra 
glenoidalia),  and  the  interarticular  cartilages  (jne7tisci). 


—   Hyaline  cartilage. 


Striated  zone. 
£ Calcified  cartilage. 


Bone. 

Marrow  (fat-cells). 

Blood-vessel. 

Fig.  100. — Vertical  Section  through  the  Head  of  a  Metacarpus  of  Adult  Man.    X  50. 

Technic  No.  65. 

The  articular  cuds  of  the  bones  are  covered  by  a  stratum  of  hyaline 
cartilage  from  0.2  to  5  mm.  thick,  thinning  toward  the  edges.  In  the 
superficial  parts  the  cartilage  cells  are  flattened  and  placed  parallel  to  the 
surface  ;  those  in  the  median  parts  are  rounded  *  and  are  often  united  in 
groups  ;  in  the  deepest  portions  the  groups  of  cells  are  partly  arranged 
in  longitudinal  rows,  vertical  to  the  surface  of  the  bone  ;  following,  but 
separated  by  a  narrow  striated  belt,  is  a  small  zone  of  calcified  cartilage 


*  The  cells  of  the  articular  cartilages  have  been  described  as  having  processes  which 
extend  into  the  adjacent  cartilaginous  matrix.  The  flattened  cartilage  cells  of  the  deeper  por- 
tions are  said  to  possess  lobulated  nuclei. 


THE    SKELETAL    SYSTEM. 


167 


interposed  between  and  connecting  the  hyaline  cartilage  and  the  osseous 
tissue  (Fig.  100). 

Not  all  the  articular  cartilages  exhibit  the  structure  just  described  ; 
the  cartilages  of  the  costo-vertebral,  the  sterno-clavicular,  the  acromio- 
clavicular, and  the  maxillary  articulations,  and  the  head  of  the  ulna  are 
not  hyaline,  but  fibro-cartilage  ;  the  distal  articular  surface  of  the  radius 
is  covered  with  dense  fibrous  tissue. 

The  glenoid  ligaments  and  the  interartictilar  cartilages  do  not  exhibit 
the  characteristic  cartilage  matrix  ;  they  consist  of  a  compact  fibrous 
connective  tissue  and  partly  of  spherical  cells.  To  the  same  category 
belong  the  so-called  sesamoid  cartilages.  The 
tendon  sheath  of  the  cuboid  bone,  however, 
contains  genuine  cartilage. 

In  the  adult  nerves  and  blood-vessels  are 
wanting  in  the  articular  cartilages,  also  in  the 
interarticular  cartilages  and  the  glenoid  liga- 
ments. 

The  joint  capsules  consist  of  an  exter- 
nal fibrous  layer,  stratnm  fibrosuvi,  varying 
greatly  in  thickness  and  possessing  a  structure 
like  that  of  the  ligaments  above  described,  and 
of  an  internal  membrane,  the  stratum  syiio- 
viale,  the  free  inner  surface  of  which  is  smooth 
and  glossy.  The  outer  layer  of  the  latter  is 
composed  of  loose  elastic  fibers  and  fibrillar 
connective  tissue,  here  and  there  containing 
fat-cells  ;  within  this  is  a  thin  lamella  of  par- 
allel connective-tissue  bundles,  in  which,  to- 
ward the  joint  cavity,  there  are  small  spherical 

or  stellate  cells,  11  to  17  ^  in  size,  containing  a  large  nucleus.  These 
cells  are  sometimes  few  in  number, — at  points  subjected  to  pressure — 
sometimes  very  abundant  and  form  distinct  epithelial  (endothelial)  layers, 
covering  the  inner  surface  with  a  three  or  four-fold  stratum. 

The  synovial  membrane  {stratum  synoviale)  often  forms  folds  con- 
taining fat  and  projecting  into  the  synovial  cavity  and  on  its  free  surface 
bears  the  synovial  villi  (Fig.  lOi),  variously  shaped  processes,  mostly  of 
microscopic  size,  which  are  particularly  closely  set  on  the  edges  of  the 
joint-surfaces  and  bestow  upon  the  synovial  membrane  a  reddish,  velvety 
appearance.  They  consist  of  connective  tissue  and  are  covered  with 
a  single  or  double  layer  of  epithelial  cells. 

The  larger  blood-vessels  of  the  synovial   membrane   lie  in  the  loose 


Fig.  ioi. — Synovial  Villi  with 
Blood-vessels  from  a 
Human  Knee-joint.  X  50. 
The  epithelium  has  fallen  from 
the  apex  of  the  left  villus,  ex- 
posing the  connective  tissue. 
Technic  No.  66. 


1 68  HISTOLOGY. 

connective-tissue  layer  ;  from  here  capillaries  extend  through  the  inner 
thin  connective -tissue  stratum  and  penetrate  Mdthin  the  villi.  Some  of 
the  villi  are  nonvascular.  The  lymph-vessels  lie  close  under  the  epi- 
thelium. 

The  nerves  run  in  the  loose  connective-tissue  stratum  and  in  part 
terminate  in  lamellar  corpuscles  (see  End-bulbs). 

The  synovia  contains  more  or  less  profoundly  altered  cells,  frag- 
ments of  cells,  and  oil  globules,  all  products  of  a  physiologic  process  of 
waste  of  the  surfaces  of  the  synovial  membrane  and  the  articular  car- 
tilage ;  also,  albumin,  mucus,  and  salts  ;  these  solid  constituents  amount 
only  to  six  per  cent.,  the  remainder  consists  of  water. 

The    Cartilages. 

The  costal  cartilages  are  of  the  hyaline  variety  ;  the  matrix  exhibits 
the  peculiarities  previously  described  (p.  96),  the  cells  frequently  contain 
fat.  Their  surface  is  enveloped  by  a  compact  fibrous  membrane,  the 
perichondrium,  which  consists  of  interlacing  connective-tissue  bundles 
and  elastic  fibers. 

The  articular  cartilages  are  covered  by  the  perichondrium  only  on 
their  lateral  surfaces,  not  on  their  contiguous  surfaces.  Where  the  car- 
tilage and  the  perichondrium  are  in  contact  there  is  a  gradual  transition 
of  the  one  tissue  into  the  other  and  consequently  the  attachment  between 
the  two  is  very  firm. 

The  perichondrium  carries  the  nerves  and  the  blood-vessels  ;  the 
latter  also  run  within  growing  cartilage,  in  buried  canals.  In  the  adult 
cartilage  is  non-vascular  ;  the  nutrition  of  the  tissue  depends  upon  diffu- 
sion from  the  surface.  In  advanced  life  the  costal  cartilages  often  con- 
tain blood-vessels  because  of  beginning  ossification. 

The  cartilages  of  the  special-sense  organs  and  of  the  respiratory 
organs  will  be  described  in  the  respective  chapters. 

The  Development  of  the  Bones. 
The  bones  are  relatively  late  structures  to  appear.  The  develop- 
ment of  the  muscles,  nerves,  vessels,  brain,  spinal  cord,  etc.,  is  already 
well  advanced  in  an  embryonal  period  when  not  a  trace  of  bone  is  pres- 
ent. At  that  time  the  skeleton  of  the  body  is  formed  of  hyaline  carti- 
lage. With  the  exception  of  certain  parts  of  the  cranium  and  nearly  all 
the  bones  of  the  face,  the  future  osseous  skeleton  is  represented  in 
cartilage.  For  example,  in  the  upper  extremity  the  humerus,  radius, 
ulna,  carpus,  and  skeletal  parts  of  the  hand  consist  of  cartilaginous 
pieces  that  are  not  hollow  like  the  bones  by  which  they  are  subsequently 


THE    SKELETAL    SYSTEM.  1 69 

replaced,  but  are  solid  throughout.  The  osseous  skeleton  then  gradually 
appears  in  the  place  of  the  cartilaginous  skeleton.  All  the  osseous 
parts  that  in  the  embryo  were  preceded  by  cartilage  are  called  primary 
or  endochondral  bone  ;  the  other  bones,  which  have  no  cartilaginous  pre- 
cursors, are  named  secondary  or  connective-tissue  bone. 


Hvaline  cartilage. 


Osteoblastic  tissue. 


Center  of  calcification. 


Primordial  marrow 
space. 


Perichondral  bone. 


Fig.  102. — From  a  Dorso-palm.\r  Longitl"din.al  Section  of  a  Ph.\lan.\  of  the  Little  Finger  of  a 
Human  Fetus  Six  Months  Old.  X  60.  At  the  center  of  calcification  the  lacunas  are  enlarged  and 
contain  several  cells;  above  the  cartilage  cells  stand  in  groups.  Each  group  has  arisen  through  the 
repeated  division  oi  one  cartilage  cell.     Technic  No.  67. 

The  pnmary  bones  include  all  the  bones  of  the  trunk  and  the  extremi- 
ties, the  greater  part  of  the  base  of  the  cranium  (the  occipital  bone  with 
the  exception  of  the  upper  portion  of  the  tabular  part,  the  sphenoid  bone 
with  the  exception  of  the  internal  pterygoid  plate,  the  temporal  bone 
and  the  ossicles  of  the  ear,  the  ethmoid  bone,  the  inferior  turbinal),  and 
the  hyoid  bone. 


170 


HISTOLOGY. 


The  secondary  bones  include  the  bones  forming  the  sides  and  roof 
of  the  cranium  and  nearly  all  the  bones  of  the  face. 

DEVELOPMENT    OF    PRIMARY    BONE. 

Here  two  processes  of  bone-formation  are  to  be  considered  :  (i)  en- 
dochondral formation,  formation  of  osseous  tissue  within  the  cartilage 
present ;  (2)  periosteal  (better  perichondral )  formation,  formation  of  osse- 


Enlarged  cartilage  cells. 


Blood-vessel  with  colored 
blood-cells. 


Endochondral  bone. 


Perichondral  bone. 


Periosteum. 


Calcified  cartilage  matrix. 


Irregular  process  of  calcified 
cartilage  matrix. 


Marrow  space. 


Perichondral  bone. 


Fig.  103.— From  a  Dorso-palmar  Longitudinal  Section  of  a  Middle-finger  Phalanx  of  a  Human 
Fetus  Four  Months  Old.    X  60.    Technic  No.  67. 

ous  tissue  immediately  surrounding,  therefore  upon,  the  cartilage.  The 
phylogenetically  older  perichondral  ossification  usually  begins  earlier,  but 
for  didactic  reasons  will  be  described  subsequently  to  the  process  of 
endochondral  formation. 

I.  Endochondral  ossification. — The  first  indications  of  this  process 
consist  in  changes  at  certain  places  within  the  cartilage  ;  the  cells  enlarge 
and  divide,  so  that  several  He  in  one  lacuna ;  then  a  deposition  of  lime 
salts  takes  place  within  the  matrix,  in  consequence  of  which  it  becomes 


THE    SKELETAL    SYSTEM. 


171 


finely  granular  and  dull;  it  calcifies.     Such  places  can  soon  be  recognized 
by  the  unaided  eye,  and  are  called  centers  of  ossification  (better,  centers 


Osteoblastic 
tissue. 


Hyaline  carti- 
^lage  (cells  in 
groups). 


Osteoblasts. 


Osteoblasts. 


Endochondral  bone. 
Marrow- 
cells. 

Fig.  104.— From  a  Longitudin.\l  Section  of  the  Phalanx  of  the  First  Finger  of  a  Human 
Fetus  of  Four  Months.  X  220.  In  the  endochondral  bone  irregular  lacunas  with  bone  cells  are 
seen.     Technic  No.  67. 


of  calcification,  Fig.  102).  The  portions  of  the  cartilage  most  remote 
from  the  center  of  calcification  continue  to  grow  in  thickness  and  length, 
while  at  the  center  growth  ceases  and  consequently  the  cartilage  at  this 


1/2 


HISTOLOGY. 


point  appears  constricted  (Fig.  102).  Meanwhile,  on  the  surface  of  the 
center  of  calcification  a  tissue  rich  in  blood-vessels  and  young  cells,  the 
osteoblastic  tissue,  has  made  its  appearance.  This  penetrates  into  the 
cartilage  and  causes  the  destruction  of  the  calcified  matrix ;  the  cartilage 
cells  are  set  free  and  degenerate.  In  this  way  a  little  excavation  arises 
in  the  center  of  calcification  ;  it  is  called  the  primary  marrow  cavity. 

These  processes  are  repeated  in  the  immediately  surrounding  carti- 
lage ;  that  is,  the  cartilage  ground  substance  calcifies,  the  cartilage  cells 
enlarge,  new  portions  of  the  cartilage  break  down,  and  as  a  result  the 


Blood-vessel.    Marrow. 


h'    h 


h  h' 


^^-^^\fv 


Blood-vessel. 


Endochondral 
bone. 


Remnants  of 
calcified  car- 
tilage matrix 


Boundary  line 
between  en- 
dochondral 
and  perichon- 
dral bone. 

Periosteum. 


Fig.  105. — Cross-section  of  the  Upper  Half  of  the  Diaphvsis  of  the  Humerus  of  a  Human 
Embryo  of  Foui*  Months,  h.  Developing  haversian  spaces;  h\  blood-vessel.  X  35-  Technic 
No.  67. 


primary  marrow-space  is  gradually  and  continuously  enlarged.  At  the 
same  time  the  capsules  of  many  cartilage  cells  are  opened,  the  cells  degen- 
erate, and  the  intervening  calcified  matrix  projects  into  the  marrow-space 
in  the  form  of  irregular  processes  (Fig.  103).  The  marrow  cavity  is  now 
a  bay-like  space,  filled  with  blood-vessels  and  with  primary  bone-marrow, 
that  is,  with  anastomosing,  branched  connective-tissue  cells.  Some  of 
these  cells,  the  osteoblasts,  grow  rich  in  protoplasm  and  apply  themselves 
in  the  manner  of  a  one-layered  epithelium  to  the  walls  of  the  marrow 
cavity  and  there  produce  bone  {cf.  p.  100).     Meanwhile,  leucocytes  appear 


THE    SKELETAL    SYSTEM. 


173 


in  ever  increasing  numbers  and  finally  form  the  chief  mass  of  the  cellular 
elements  of  bone-marrow,  therewith  converting  the  primary  marrow 
into  the  red  marrow. 

Some  of  the  branched  connective-tissue  cells  retain  their  form  and  later 
together  with  a  fine-fibered  connective  tissue  constitute  the  supporting  frame- 
work of  the  bone-marrow.      Others  of  these  cells  become  fat-cells. 

Through  the  activity  of  the  osteoblasts  the  marrow  cavity  is  soon 
clothed  with  a  thin  stratum  of  bone  gradually  increasing  in  thickness  ; 
the  irregular  processes  of  calcified  ground  substance  are  completely  en- 
veloped in  young  bone.      Thus  step  by  step  the  former  solid  piece  of 


Ostoclast. 


Bone. 


;o«if 


Indifferent  formative 
cells  of  the  peri- 
osteum. 


t 


Cartilage. 


Fig.  106. — From  a  Section  of  the  Hard  Palate  of  a  Newborn  Kitten.     X  240.    Techiiic  No.  67. 

cartilage  is  transformed  into  spongy  bone,  the  trabeculse  of  which  still 
contain  residues  of  calcified  cartilage  matrix  (Fig.  105). 

2.  PericJioidral  ossification.  This  process  of  bone  formation  is 
likewise  performed  by  the  osteoblasts  derived  from  the  osteoblastic  tissue 
at  the  surface  of  the  center  of  calcification  (Fig.  102).  Through  the 
activity  of  the  osteoblasts  *  strata  of  plexiform  osseous  tissue  are  periodi- 
cally formed  on  the  surface  of  the  cartilage  (Fig.  103)  ;  these  osseous 
masses  are  distinguished  from  the  endochondral  bone  by  the  absence  of 
reinnants    of   calcified  cartilaginous    matrix,   because    the    perichondral 

*  In  the  inner  strata  of  the  perichondral  osseous  cortex  the  osteoblasts  are  almost  entirely 
absent;  also  in  the  region  of  the  endochondral  osseous  trabecular  the  number  of  osteoblasts  is 
smaller,  which  doubtless  is  associated  with  the  future  process  of  resorption. 


1/4  HISTOLOGY. 

bone  is  formed  at  the  circumference  and  not  in  the  interior  of  the  cartilage. 
The  formation  of  the  first  haversian  canals  may  be  studied  in  the  peri- 
chondral bone  (Fig.  105).  The  latter  is  not  formed  in  a  continuous  layer 
of  uniform  thickness,  but  at  frequent  intervals  depressions  may  be 
observed  containing  blood-vessels  surrounded  by  osteoblasts  (Fig.  105, 
li,  h)  ;  at  first  the  depressions  are  mere  furrows  open  toward  the  per- 
iphery, but  with  the  progressive  development  of  the  perichondral  osseous 
strata  they  are  closed  in  (/^'),  and  then  represent  vascular  canals,  the 
haversian  canals.  The  osteoblasts  enclosed  within  the  canals  produce 
new  osseous  strata,  the  future  haversian  lamellae  (Fig.  108). 

By  the  absorption  of  the  cartilage  and  its  substitution  by  osseous 
tissue  (endochondral  ossification)  and  by  the  deposition  of  bone  substance 
on  its  exterior  (perichondral  ossification)  the  piece  of  cartilage  has 
become  a  bone. 

The  essence  of  the  foregoing  processes  consists  in  an  absorption  of  the 
parts  of  the  primordial  skeleton  and  in  a  reconstruction  of  the  same  by  the 
development  of  bone  substance.  This  mode  of  bone  formation  is  termed  the 
neoplastic  type.  On  the  articular  fossa  of  the  temporal  bone,  on  the  suture  of 
the  palate,  on  the  inferior  maxilla,  on  the  tuberosity  of  the  radius,  on  the 
spine  of  the  scapula,  and  on  the  tips  of  the  terminal  phalanges  areas  are  found 
in  which  apparently  a  direct  transformation  of  cartilage  into  bone  takes  place 
(Fig.  106).  From  this  the  conclusion  has  been  deduced  that  here  a  direct 
metamorphosis  of  the  matrix  of  cartilage  into  the  matrix  of  bone,  of  cartilage 
cells  into  bone-cells,  occurs  and  the  process  has  been  named  the  metaplastic 
type.  The  conclusion  is  unwarrantable  ;  it  is  not  here  a  question  of  the 
metamorphosis  of  a  developed  cartilage  cell  into  a  bone-cell,  but  of  the  per- 
formances of  indifferent  formative  cells  of  the  periosteum,  that  sometimes  pro- 
duce cartilage,  sometimes  bone  (see  also  p.  100,  remark  *).  Bones  that  exhibit 
a  metaplastic  type  are  in  their  original  anlage  either  perichondral  or  connec- 
tive-tissue bones. 


DEVELOPMENT    OF    SECONDARY    OR    CONNECTIVE-TISSUE    BONE. 

Here  the  foundation  on  which  the  formation  of  bone  occurs  is  not 
cartilage,  but  connective  tissue.  Isolated  bundles  of  connective  tissue 
calcify  ;  on  these  osteoblasts  (Fig.  107)  derived  from  embryonal  cells  ar- 
range themselves  and  produce  bone  in  the  manner  previously  described. 
Or  small  groups  of  osteoblasts  can  secrete  calcified  substance,  that  be- 
comes the  stardng  point  for  the  development  of  osseous  trabeculas.  For 
the  comprehension  of  connective-tissue  bone  it  is  necessary  to  bear  in 
mind  that  it  is  surrounded  on  all  sides  by  connective  tissue  ;  when 
osseous  tissue  is  in  contact  on  one  side  with  cartilage,  without  the  inter- 
position of  connective  tissue,  the  resulting  formation  is  not  connective- 
tissue  bone,  but  perichondral  bone. 


THE    SKELETAL    SYSTEM. 


175 


THE    GROWTH    OF    BONES. 

I .  Bones  preformed  in  cartilage. 
{a)  In  tubular  bones  ossification  in  the  diaphysis  begins  much  earlier 
than  in  the  epiphyses  (in  the  humerus  the  center  of  ossification  in  the  diaph- 
ysis appears  in  the  eighth  fetal  week,  in  the  epiphyses  in  the  first  year 
of  life) ;  blood-vessels  grow  into  the  calcified  cartilage,  which  at  first  is 
transformed  only  by  endochondral,  later  also  by  perichondral  ossification 
into  bone.  The  articular  surfaces  of  the  bone  remain  permanently  carti- 
laginous ;  a  temporary  narrow  zone  of  cartilage  between  diaphysis  and 
epiphysis,  the  epipliyseal  cartilage,  persists  until  the  growth  of  the  bone 


Osteoblasts. 


Calcifying  connective- 
tissue  bundles. 


Bone-cells. 


Fig.  107. — From  a  Section  of  the  Inferior  Maxilla  of  a  Human  Fetus  Four  Months  Old. 

X  240.     Technic  No.  67. 

is  completed.  Here  an  active  growth  of  cartilage  occurs  that,  by  ex- 
tension of  the  primary  marrow  cavities  of  the  diaphysis  and  the  epi- 
physes, is  continually  being  supplanted  by  bone.  In  this  way  the  bone 
grows  in  length.  Increase  in  thickness  takes  place  by  the  constant 
"  apposition  "  of  new  periosteal  strata  of  bone.* 

{B)  In  sJiort  bones  ossification  takes  place,  as  in  the  epiphyses,  at 
first  by  endochondral  ossification  ;  after  the  absorption  of  the  last  super- 
ficial remnant  of  cartilage  a  perichondral  osseous  cortex  is  formed. 

{c)  \n  flat  bones  ossification  is  first  perichondral,  then  endochondral. 

2.    Connective-tissue  bones. 
These  grow  in  superficies  and  in  thickness  by  the  formation  of  new 


*  "  Interstitial  "  growth,  dependent  on  increase  of  the  ground  substance  between  the  bone 
lacunre,  occurs  only,  in  very  slight  degree,  in  the  youngest  bone  substance.  The  bone-cells  are 
much  more  numerous  here  than  in  later  stages. 


176  HISTOLOGY. 

osseous  masses  at  their  edges  and  on  their  surfaces  respectively.  As  a 
consequence  of  the  abundant  deposition  of  bone-substance  on  the  sur- 
faces, the  outer  and  inner  tables  of  compact  bone  are  formed,  which  en- 
close between  them  spongy  bone  ;  the  latter  in  this  situation  is  termed 
diploe.  The  osseous  masses  at  first  possess  a  coarse-fibered,  later  (from 
about  the  first  year  of  life)  a  fine-fibered  matrix  (p.  98). 


.^*.^< 


m  ^ftJ^^  '  '  ■      '        '  ^^^  Haversian  canals  in  the 


.  Jim 


f»l€ 


9  » 


^i'h^ 


§ 


Osteoblasts. 

aversian  ca 

process  of  formation. 


Blood-vessels. 
Perichondral  bone. 


5  ^       Finished  haversian 

'V-^--  canal. 


¥ 


'Jfc'  __    Empty  lacunae. 


)>r'^tx-    7" 


■i>  >- ■-- 


%tR    |«^-%'«i*-...^|_,.,  Ostoclast. 


'  Endochondral  border- 

___— — :r-'  line. 

-'  ^  ~     Endochondral  bone. 


Fig.  108.— Portion  of  a  Cross-section  of  a  Tubular  Boke  of  a  Newborn  Kitten.    Technic  No.  67. 


THE    RESORPTION    OF    BONES. 

Simultaneously  with  the  first  anlage  of  osseous  tissue  a  counter 
process,  resorption,  becomes  noticeable,  by  which  the  calcified  cartilage 
matrix,  as  well  as  many  parts  of  the  recently  formed  bone,  is  dissolved. 
Resorption  occurs  in  slight  measure  in  flat  and  in  short  bones  and  on 
the  surface  of  all  bones  until  their  typical  shape  is  developed,  but 
in  extremest  degree  in   tubular  bones,  in  the  formation  of  the  marrow 


THE    SKELETAL    SYSTEM.  I  77 

cavity.*  In  this  process  not  only  entire  masses  of  endochondral  bone  t 
are  lost,  but  also  conspicuous  quantities  of  perichondral  bone,  losses 
that  are  always  covered  by  deposition  from  outside  of  strata  of  new 
perichondral  bone.  Also  in  the  interior  of  the  substantia  compacta  irreg- 
ular cavities  are  seen,  the  so-called  Jiaversian  spaces,  that  have  arisen  by 
solution  of  the  inner  haversian  lamellae,  which  may  become  partially 
filled  again  by  deposition  of  new  osseous  masses  (Fig.  96,  li).  The 
substantia  spongiosa  of  the  bone  of  adults  arises  by  resorption  from  the 
marrow  cavity  and  from  the  inner  surface  of  the  haversian  canals,  which 
leads  to  the  gradual  reduction  of  the  bone  to  small  strips,  the  trabeculae 
and  lamellae  of  the  spongy  substance. 

In  all  places  where  the  resorption  of  bone  occurs  the  ostoclasts 
(bone  destroyers,  p»  163)  are  seen,  lying  in  pit-like  depressions  {^How- 
ship's  laciincB)  in  the  bone. 

Even  in  the  fully  developed  skeleton  the  processes  of  apposition 
and  resorption  still  continue  in  a  few  localities. 

TECHNIC. 

No.  61. — Ground  sections  of  dried  bone. — The  bone  must  not  be 
dried  before  maceration,  but  must  be  placed  fresh  for  several  months  in 
water,  which  should  be  frequently  changed.  Then  it  is  dried  and  a  piece 
held  between  two  pieces  of  cork  or  folds  of  cloth  is  clamped  in  a  vice 
and  a  section  i  or  2  mm.  thick,  transverse  or  longitudinal,  is  cut  with  a 
compass-saw.  Glue  the  section  with  sealing-wax  to  the  under  surface 
of  a  cork-stopper  (the  sealing-wax  should  encircle  the  section),  dip 
the  whole  for  a  moment  in  water  and  then  file  it,  first  with  a  coarse, 
then  with  a  fine  file,  until  it  is  perfectly  smooth  ;  the  file  must  be  fre- 
quently dipped  in  water,  in  order  to  wash  off  the  adherent  particles  of 
bone  and  to  prevent  the  heating  of  the  sealing-wax  by  friction. 

The  section  of  bone  should  then  be  loosened  by  heating  the  seal- 
ing-wax and  the  smooth  side  stuck  fast  to  the  stopper.  It  must  now  be 
filed  until  it  is  so  thin  that  the  sealing-wax  can  be  seen  through  it.  The 
whole  should  at  once  be  placed  in  90  per  cent,  alcohol,  in  which 
within  a  few  minutes  the  section  becomes  loosened  from  the  cork. 
Then  moisten  a  coarse  whetstone  with  water,  rub  it  with  a  second 
whetstone  until  the  surface  is  covered  with  a  little  grinding-paste  ;  lay 
the  section  in  the  paste,  place  on  it  a  smooth  cork  (one  without 
cracks),  and  with  a  circidar  motion  grind  it  on  both  sides  ;  it  is  not  nec- 
essary to  glue  the  section  to  the  cork.     The  section  when  sufficiently 

*  For  example,  a  femur  of  a  three-year  old  child  contains  scarcely  any  of  the  osseous 
tissue  present  at  birth. 

I  The  osseous  labyrinth  of  the  ear  forms  an  exception  ;  it  still  contains  remnants  of  cal- 
cified cartilage  even  in  extreme  old  age. 


178  HISTOLOGY. 

thin  is  transparent ;  this  is  to  be  ascertained  by  drying  it  between 
pieces  of  filter-paper  and  examining  with  the  low  power.  It  should 
then  be  ground  on  a  fine  whetstone,  in  the  same  manner  as  on  the 
coarse,  and  when  both  sides  are  smooth  it  should  be  dried  with  filter- 
paper  and  polished.  Nail  a  piece  of  wash-leather  smoothly  on  a  board, 
sprinkle  it  with  chalk,  and  with  the  tip  of  the  finger  rub  the  section 
to  and  fro  on  the  leather.  In  this  way  the  previously  dull  section 
acquires  shining  surfaces.  The  adherent  powder  may  be  removed  by 
rubbing  the  section  on  fresh  wash-leather.  The  finished  section  is  to 
be  placed  dry  on  a  slide  and  the  cover- glass  is  secured  by  means  of 
cement  (p,  50). 

Examine  first  with  the  low,  then  with  the  high  power.  The  bone 
lacunae  and  bone  canaliculi  are  filled  with  air  and  with  the  customary 
illumination  of  the  object  from  below  appear  black  (Fig.  47).  If  the 
section  is  thick  it  may  be  impossible  to  examine  it  with  the  high 
power,  since  then  the  objective  cannot  be  brought  near  enough  to  the 
preparation. 

No.  62. — Sharpef  s  fibers. — Prepare  a  cross-section  of  the  middle 
of  the  shaft  of  a  tubular  bone,  preferably  of  a  young  individual,  accord- 
ing to  the  method  given  in  No.  61.  Place  the  finished  dry  section  for 
from  two  to  five  minutes  in  4  c.c.  of  xylol  and  then  mount  in  xylol- 
balsam.  The  fibers,  invisible  in  the  sections  produced  by  other  methods 
(No.  61  and  No.  63),  can  be  plainly  seen,  even  with  the  lower  power 
(Fig.  99). 

No.  63. — Haversian  canals  and  bone  lamell(E. — Select  the  meta- 
carpal bone  of  an  adult ;  after  four  weeks'  fixation  in  Miiller's 
fluid  and  hardening  in  alcohol,  decalcify  in  from  3  to  9  per  cent, 
nitric  acid  (p.  36),  harden  again,  and  cut  transverse  and  longitu- 
dinal sections.  The  compact  structure  of  larger  bones  (the  femur, 
for  example)  requires  too  much  time  (several  weeks)  for  decalcification. 
The  periosteum  should  be  allowed  to  remain  on  the  bone.  For 
longitudinal  views  of  haversian  canals  very  thick  sections  (0.5  mm.  or 
more)  must  be  made.  Mount  in  dilute  glycerol  (Fig.  95),  Nor  are 
very  thin  sections  necessary  for  transverse  cuts  of  the  canals  and  lamel- 
lar systems ;  the  lamellae  are  best  seen  if  the  section  be  examined  in  a 
drop  of  distilled  water  and  the  mirror  turned  so  that  the  object  is  only 
half  illuminated  ;  in  this  way,  too,  the  striae  produced  by  the  bone  canal- 
iculi, running  vertically  to  the  lamellae,  are  best  seen  (Fig.  96).  Mount 
in  dilute  glycerol,  which,  however,  makes  the  lamellar  systems  partially 
indistinct.  Not  every  part  of  the  bone  exhibits  all  the  lamellar  systems  ; 
the  outer  and  also  the  inner  ground  lamellae  are  frequently  wanting.  In 
sections  taken  near  the  epiphyses  the  transition  of  the  compact  substance 
into  the  trabeculae  of  the  spongy  bone  can  be  seen.  The  bone  lacunae 
and  bone  canaliculi  are  much  less  distinct  in  moist  preparations  than  in 
dried  ground  sections,  because  the  contained  air  has  been  displaced  by 
the  mounting  medium.      (Compare  Fig.  47  with  Fig.  48.) 

Not   infrequently  the   concentric  lamellae   of  the  haversian  systems 


THE    SKELETAL    SYSTEM.  1/9 

are  found  to  be  interrupted  by  an  irregular  line,  the  rcsorptioii  line.  Up 
to  this  line  the  osseous  tissue  previously  formed  has  been  again  resorbed 
(p.  176).  All  that  which  lies  within  the  line  is  newly  deposited  bone- 
substance.  These  formations  are  partially  filled  haversian  spaces  (Fig. 
96,  h). 

No.  64. — Red  boiie-viarrozv. — {a)  Compress  the  halved  vertebra  or 
the  rib  of  a  calf  in  a  vice  or  with  tongs  ;  with  a  pipet  take  up  a  small 
drop  of  the  liquid  thus  expressed,  transfer  it  to  a  slide  and,  without  the 
addition  of  any  other  fluid,  apply  a  small  cover-glass  or,  better,  a  frag- 
ment of  a  cover-glass.  Examined  with  the  high  power  red  blood-cells, 
hematoblasts,  marrow  cells  of  different  sizes,  and  giant  cells  will  be 
seen,  but  not  always  their  nuclei  (Fig.  109,  i).  Add  a  drop  of  picro- 
carmine  (p.  53) ;  the  nuclei  become  red  in  from  one  to  two  minutes,  but 
are  still  pale  (Fig.  109,  2).  If  the  picrocarmine  is  displaced  by  salt 
solution  and  this  by  dilute  acidulated  glycerol,  the  nuclei  acquire  a  deep 


A- 

b       0X^ 

0  ^ 

0  ^'  M" 

Q    ^  0 

°o^®ji4) 

Fig.  109. — Isolated  Elements  of  Fresh  Bone-marrow  from  the  Vertebra  of  a  Calf.  >C  560. 
I.  In  salt  solution.  2.  Stained  with  picrocarmine.  3.  After  treatinent  with  acidulated  glycerol,  i. 
Marrow  cells  ;  k',  two  marrow  cells  containing  masses  of  pigment-granules,  the  cell  on  the  right  seen 
from  the  side,  the  cell  on  the  left  seen  from  the  surface;  b,  nonnucleated  colored  blood  corpuscles; 
?•,  megakaryocytes  ;  in  the  one  on  the  right  the  nucleus  is  dividing  by  constriction,  at  two  lateral 
points  and  at  X  on  the  surface. 

color  and  sharp   contours  (Fig.   109,    3).      Occasionally   giant-cells    are 
sought  in  vain.      Human  ribs  are  often  usable. 

(^)  For  permanent  preparations  proceed  as  follows  :  With  a  t/iiu 
cover-glass  take  up  a  drop  of  the  marrow  expressed  from  a  rib  and  make 
two  cover-glass  preparations  as  directed  in  No.  45,  for  dry  cover-glass 
preparations  of  blood,  after  Ehrlich.  Since  the  marrow  does  not  diffuse 
as  readily  as  blood  between  the  two  cover-glasses,  make  slight  pressure 
upon  them  before  slipping  them  apart,  by  means  of  forceps.  They 
should  not  be  allowed  to  dry,  but  should  be  placed  at  once  in  a  concen- 
trated aqueous  solution  of  corrosive  sublimate  (5  gm.  in  100  c.c.  of 
distilled  water).  At  the  end  of  ten  minutes  transfer  them  to  200  c.c.  of 
distilled  water,  which  is  to  be  changed  in  about  five  minutes.  In  another 
ten  minutes  place  them  in  5  c.c.  of  diluted  eosin  (p.  39,  3  b)  for  from  one 
to  five  minutes,  then  wash  for  a  moment  in  distilled  water  and  transfer 
them  to  5  c.c.  of  filtered  Hansen's  hematoxylin;  after  a  minute  or  two 
place  them  for  five  minutes  in  distilled   water  ;    remove   the   water   by 


l8o  HISTOLOGY. 

means  of  filter-paper  placed  at  the  edge  of  the  cover-glass  and  place  them 
in  95  per  cent,  alcohol  (not  longer  than  one  minute,  lest  the  eosin  be 
extracted),  then  in  carbol-xylol  for  three  minutes.  With  a  cloth  care- 
fully remove  the  oil  from  the  film-free  surface  of  the  cover-glass,  place  a 
drop  of  xylol-balsam  on  the  surface  containing  the  film  of  marrow,  and 
invert  the  cover-glass  on  a  slide.  The  colored  blood-cells,  which  are 
very  often  distorted,  and  the  protoplasm  of  the  hematoblasts  are  stained 
a  brilliant  rose  color,  the  protoplasm  of  the  remaining  cells  gray-violet ; 
all  the  nuclei  are  blue.  Cells  containing  oxyphile  (eosinophile)  granules 
are  often  found  (Fig.  97).  Cells  with  neutrophile  and  basophile  granules 
are  exhibited  by  treating  bone-marrow  according  to  technic  No.  45. 

No.  65. — Articular  cartilage. — Select  the  head  of  the  metacarpal 
bone  of  an  adult  and  treat  it  according  to  the  method  given  in  No.  63. 
Cut  longitudinal  sections  and  mount  them  in  dilute  glycerol  (Fig.  100). 
The  parallel  streaks  often  present  in  the  hyaline  cartilage  are  produced 
by  the  razor.  The  granules  of  the  calcified  cartilage  disappear  in  the 
process  of  decalcification. 

No.  66. — Synovial  villi. — From  a  cadaver,  as  fresh  as  possible,  cut 
out  a  piece  about  4  cm.  square  of  the  capsular  ligament  at  the  border  of 
the  patella,  and  with  the  scissors  take  off  a  strip  2  or  3  mm.  broad  from 
the  reddish,  glossy,  velvety  inner  surface  of  the  same,  moisten  it  with  a 
drop  of  salt  solution,  and  without  a  cover-glass  examine  it  with  the  low 
power.  At  the  edges  of  the  strip  the  villi  can  be  seen  ;  their  blood-ves- 
sels often  still  contain  blood-cells.  The  shining  nuclei  of  the  epithelial 
cells  he  close  beside  one  another  (Fig.  loi). 

If  it  is  desired,  the  preparation  may  be  stained  under  the  cover-glass 
with  picrocarmine  and  mounted  in  diluted  glycerol  (p.  5  3),  but  much  of 
the  original  beauty  is  lost. 

No.  67. — Development  of  bone. — Human  embryos  four  or  five 
months  old,  embryos  of  the  sheep,  pig,  or  cow,  from  10  to  14  cm.  long 
(measured  from  the  tip  of  the  snout  to  the  root  of  the  tail),  are  suitable. 
The  latter  are  readily  obtained  at  the  slaughter-house  ;  the  entire  uterus 
should  be  ordered.  Place  parts  of  the  human  embryos,  the  animal 
embryos  in  toto  (2  or  3  in  i  liter),  in  Zenker's  fluid  for  forty -eight  hours. 
Wash  in  running  water  for  forty-eight  hours  and  harden  in  from  200  to 
400  c.c.  of  gradually  strengthened  alcohols  (p.  35).  After  the  embryos 
have  lain  one  week  or  longer  in  90  per  cent,  alcohol  containing  tincture 
of  iodin  (p.  33),  cut  off  the  head,  the  extremities  close  to  the  rump,*  and 
decalcify  them  in  200  c.c.  of  distilled  water  to  which  2  or  4  c.c.  of  pure 
nitric  acid  have  been  added.  In  from  two  to  five  days,  during  which 
the  decalcification  medium  must  be  changed  about  three  times,  the 
extremities  are  to  be  taken  out  (the  head  is  probably  not  yet  decalcified, 
and  must  remain  in  two  per  cent,  nitric  acid  for  several  days  more), 
treated  with  potassium* alum  (p.  36)  then  washed  from  one  to  six  hours 

*  Pieces  of  the  vertebral  column  and  the  ribs  likewise  yield  instructive  pictures. 


THE    SKELETAL    SYSTEM,  151 

in  running  water,  and  again  hardened  in  gradually  strengthened  alcohols. 
After  they  have  lain  five  days  in  90  percent,  alcohol,  cut  the  extremities 
into  pieces  i  cm.  long,  which,  should  they  still  be  too  soft,  may  be 
placed  for  one  or  two  days  in  30  c.c.  of  absolute  alcohol. 

For  sections  showing  the  Jirst  /processes  in  the  development  of  bone 
(Fig.  102-104),  embed  in  liver  the  phalanges  and  metacarpal  bones  (the 
latter  are  very  long  in  the  animals  mentioned),  and  make  longitudinal 
(sagittal)  sections,  from  the  flexor  to  the  extensor  surface  ;  to  be  useful 
the  sections  must  be  taken  in  the  axis  of  the  extremities,  those  taken 
from  the  margin  exhibit  pictures  that  are  unintelligible. 

For  7no7^e  advanced  stages  make  chiefly  transverse  sections  of  the 
humerus  and  femur.  Sections  through  the  diaphysis  show  more  peri- 
chondral, sections  through  the  epiphyses  more  endochondral  bone. 

The  most  beautiful  osteoblasts  are  obtained  in  cross-sections  of  the 
inferior  maxilla,  which  are  also  valuable  as  preparations  showing  the 
development  of  teeth. 

For  still  later  stages  the  skeleton  ol  newborn  animals  is  useful  ; 
their  phalanges  show  tolerably  early  stages  in  the  process,  their  carpal 
bones  the  first  stages.  The  decalcification  requires  somewhat  more  time 
(up  to  eight  days). 

For  connective-tissue  bone  select  the  parietal  and  frontal  bones  01 
embryos  and  cut  horizontal  sections. 

All  the  sections  are  to  be  stained  in  4  c.c.  of  Hansen's  hematoxy- 
lin (p.  38)  for  from  two  to  ten  minutes,  transferred  to  10  c.c.  of  distilled 
water  for  ten  minutes,  then  stained  in  4  c.c.  of  eosin  for  one  minute  (p. 
39),  washed  for  two  minutes  in  5  c.c.  of  distilled  water,  and  mounted  in 
xylol-balsam  (p.  50). 

If  the  staining  is  successful,  the  cartilage  (especially  the  calcified 
portion)  is  blue,  the  bone  red.  Occasionally  the  cartilage  does  not  stain 
a  bright  blue  ;  then,  instead  of  using  the  usual  hematoxylin  solution, 
place  the  sections  in  5  c.c.  of  distilled  water  plus  5  drops  of  filtered 
hematoxylin  solution.  In  from  six  to  fourteen  hours  the  cartilage  will 
be  blue.  The  eosin  staining  of  bone  often  is  not  uniform  ;  the  youngest 
portions  of  the  bone,  the  margins  of  the  osseous  trabeculae,  for  example, 
are  often  the  most  brilliantly  stained. 


182 


HISTOLOGY. 


III.     ORGANS    OF    THE    MUSCULAR    SYSTEM. 

The  muscular  system  is  composed  of  a  large  number  of  contractile 
organs,  the  muscles,  which  consist  of  cross-striated  muscle  tissue  and 
are  joined  to  the  skeleton,  the  skin,  the  viscera,  etc.,  by  the  inter- 
vention of  special  connective-tissue  formations,  the  tendons,  and  by 
accessory  apparatus  of  similar  structure,  the  fascia,  tendon-sheaths,  and 
burses. 

Each  muscle  is  composed  of  striated  muscle-fibers  (p.  1 06)  that  as  a 
rule  are  united  in  such  a  manner  that  they  lie   lengthwise,  side   by  side 


Perimysium  externum. 


Muscle-bundles. 


Perimysium  internum. 


Cross-section  ofarterv. 


Muscle-spindle.       (See 
page  226.) 


Cross-section  of  nerve. 

Fig.  no. — From  a  Cross-section  of  the  Omo-hyoid  Muscle  of  Man.     X  60.    Technic  No. 


and  behind  one  another,  and  are  held  together  by  loose  connective 
tissue,  the  perhnysiuni.  Transverse  interlacing  is  rare,  but  occurs,  for 
example,  in  the  tongue.  Neighboring  muscle-fibers  never  are  in  direct 
contact  by  their  sarcolemmae,  but  each  individual  fiber  is  enveloped  in  a 
delicate  connective-tissue  sheath,  the  perimysium  of  the  single  muscle- 
fiber,  which  is  joined  to  neighbor  sheaths  (Fig.   1 1 1). 

A  somewhat  thicker  connective-tissue  sheath,  the  perimysium  inter- 
num, encloses  a  large,  widely  varying  number  of  fibers  and  in  this 
way  a  muscle-bundle  is  formed  (Fig.  i  loj.      A  collection  of  mu!^cle-bun- 


THE    MUSCULAR    SYSTEM.  I  83 

dies  *  forms  a  muscle,  the  surface  of  which  is  covered  by  a  still  thicker 
connective-tissue  sheath,  the  perim\-sium  externum.  The  several  sheaths 
are  connected  with  one  another. 

The  perimysium  is  composed  ot  fibrillar  connective  tissue  and  fine 
elastic  fibers,!  occasionally  contains  fat-cells,  and  conveys  the  nerves, 
blood-vessels,  and  lymph-vessels.  The  perimysium  of  the  individual 
muscle-fiber  contains  only  capillaries  and  terminal  branches  of  nerves. 

The  post-embryonal  increase  in  the  thickness  of  the  muscles  depends 
less  on  the  multiplication  by  division,  than  on  the  growth  in  thickness  of 
the  already  existing  muscle-fibers. 

The  tendons  are  characterized  by  the  parallel  course  of  their  fibers, 
by  their  firm  union,  and  by  their  poverty  in  elastic  fibers.  They  are 
composed    of   dense-fibered    connective-tissue    bundles,    the    "  tendon- 

Perimysium  of  tlie  individual 
Muscle-fiber.  muscle-fiber. 


X. 


Connective-tissue  sheath 


Cross-section     Muscle-fibers     Nucleus     Nucleus  of  the 
of  nerve.  of  the  of  the         sarcolemma. 

spindle,     perimysium. 

Fig.  III. — Portion  of  the  Section  of  Figure  no.  X  240. 

bundles,"  which  are  held  together  by  loose  connective  tissue.  Each  of 
these  (so-called  secondary)  tendon-bundles  consists  of  a  number  of 
parallel  fibrillae  running  a  perfectly  straight  course  and  united  by  a  small 
amount  of  cement-substance  in  smaller  (so-called  primary)  bundles. 
Between  the  primary  bundles  lie  the  cellular  elements  of  the  tendon  ; 
they  are  spindle-shaped  or  stellate,  or  four-sided,  flat  connective-tissue 
cells,  placed  behind  one  another  in  rows  ;  they  are  bent  like  concave 
tiles  and  partially  encircle  the  primary  bundles  ;  they  unite  by  means  of 
processes  with  neighbor  cells. 

Elastic  fibers  in  large  quantity  are  found  only  in  the   loose  connec- 


*  The  grouping  of  the  primary  bundles  in  secondary  bundles,  of  which  a  certain  number 
form  tertiary  bundles,  that  finally  unite  to  form  a  muscle,  is  an  arbitrary  classification  and  in 
many  preparations  cannot  be  recognized. 

t  In  the  perimysium  externum  elastic  fibers  are  present  in  great  abundance  ;  the  muscles 
of  the  extremities  are  poor,  the  diaphragm  is  rich  in  elastic  fibers. 


1 84 


HISTOLOGY. 


tive  tissue  ;  in  the  dense  tendon-bundles  they  are  very  scarce  and  occur 
in  the  form  of  a  fine,  wide-meshed  network. 


Loose  connective  tissue. 


Blood-vessel. 


Tendon  bundle. 


Loose  connective  tissue. 


Fig.  112. — From  a  Cross-section  of  a  Tendon  of  Adult  Man.    X  40.    The  dark  dots  in  the  tendon 
bundles  are  connective-tissue  cells.     Technic  No.  69. 

The   union   of   the   muscles  with  tendons  and  fibrous  membranes 
(periosteum,  fascia)  is  effected  by  an  extension  of  the  perimysium  of  the 


Elastic / 

fiber. 


Nucleus. 


Proto- 
plasm. 


1} 


^<i 


Fig.  113. — Tendons  from  a  Rat's  Tail.  X  240.  A.  Tendon-cells 
viewed  in  profile;  B,  from  the  surface.  At  X  the  nucleus  is  bent 
so  that  it  is  seen  partly  in  profile  (the  shaded  portion)  and  partly 
from  the  surface  (the  light  portion).     Technic  No.  71. 


Muscle- 
fibers.  I  /,/ 


Fig.  114. — From  a  Sagittal 
LongitudinalSection  of 
THE  Gastrocnemius  of  a 
Frog.  X  50.  The  upper- 
most mark  indicates  the 
perimysium  seen  from  the 
surface  (as  transverse 
lines).    Technic  No.  72. 


individual   muscle-fiber   into   these  structures  and   the   blending    of  the 
tissues  ;  the  sarcolemma  takes  no  part  in  this,  but  closely  investing  the 


THE    MUSCULAR    SYSTEM.  185 

muscle-fiber  terminates  as  a  closed  sac  with  pointed  or  obliquely  blunted 
ends  (Fig.  114).  The  radiating  cross-striped  muscle-fibers  in  the  skin 
attach  themselves  to  the  connective  tissue  of  the  corium  by  pointed  or 
forked  ends. 

The  fascice  in  part  exhibit  the  same  structure  as  the  tendons  and  in 
part  they  are  connective-tissue  membranes  richly  provided  with  elastic 
fibers.  The  latter  is  the  case  only  when  they  form  sheaths  for  the 
muscles  and  do  not  furnish  surfaces  for  the  attachment  of  the  muscle- 
fibers. 

The  tendon-sheaths  and  the  hnrscF  consist  of  a  layer  of  varying 
thickness  of  connective  tissue  with  elastic  fibers,  the  inner  surface  of 
which  is  covered  patcliuise  by  an  "  endothelium  "  ;  that  is*  by  a  usually 
simple  layer  of  connective-tissue  cells. 

Where  the  endothelium  is  wanting  the  connective  tissue  is  dense 
and  rich  in  rounded  elements  resembling  cartilage  cells.  The  majority 
of  the  tendon-sheaths  have  small  vascular  processes  exactly  like  the 
synovial  villi. 

The  blood-vessels  of  the  striated  muscles  are  ver\'  numerous  and 
evenly  distributed  ;  the  capillaries  are  among  the  most  delicate  in  the 
human  body  and  form  networks  characterized  by  elongated  rectangular 
meshes,  lying  immediately  upon  the  fibers.  The  veins  are  provided  with 
valves  even  in  their  smallest  branches.  The  lymph-vessels  are  few  in 
number  and  follow  the  ramifications  of  the  smaller  blood-vessels. 

For  the  nerves,  partly  sensory  and  partly  motor,  of  cross-striped 
muscle,  as  well  as  for  the  muscle-spindles,  see  the  Peripheral  Nerve- 
endings,  p.  220. 

The  blood-vessels  of  the  tendons  and  the  thinner  fascice  are  \'er}' 
scarce  and  are  found  only  in  the  loose  connective  tissue  surrounding  the 
tendon-bundles  ;  on  the  other  hand,  the  tendon-sheaths  and  the  bnrsce 
have  a  rich  v^ascular  supply.  Lymph-vessels  are  found  only  on  the  sur- 
face of  the  tendons. 

The  medullated  nerves  of  tendons  terminate  in  part  in  a  close  plexus 
of  nonmedullated  nerve-fibers  and  in  part  pass  into  spindle-shaped  expan- 
sions of  the  tendon,  the  so-called  tendon-spindles  (see  the  Peripheral 
Nerve-endings).  End-bulbs  and  lamellar  corpuscles  are  found  in  the  peri- 
mysia,  tendons,  fasciae,  and  tendon-sheaths. 

TECHNIC. 

No.  68. — Bundles  of  striped  muscle. — Select  a  muscle  in  which  the 
fibers  have  a  parallel  disposition  (for  example,  the  adductor  of  the  rab- 
bit) and  with  a  sharp  razor  make  a  deep" incision  transverse  to  the  course 


1 86  HISTOLOGY. 

of  the  fibers  and  2  or  3  cm.  below  make  a  second  incision  ;  connect  these 
by  longitudinal  incisions  and,  luithout  traction,  carefully  remove  the  piece 
thus  mapped  out.  For  fixation  place  it  in  100  c.c.  of  o.  i  per  cent,  chromic 
acid  (p.  32).  After  two  weeks  wash  it  for  2  or  3  hours  in  running  water 
and  harden  in  50  c.c.  of  gradually  strengthened  alcohols  (p.  35).  Cut 
cross-sections  and  examine  them  unstained  in  diluted  glycerol.  The 
muscle-fibers  differ  greatly  in  thickness  ;  the  very  smallest  are  sections 
through  the  ends  of  the  fibers.  Although  the  muscle-fibers  are  cylin- 
drical and  therefore  in  section  should  appear  circular,  they  have  an  irreg- 
ularly polygonal  outline  due  to  mutual  pressure.  The  perimysium  of 
the  individual  fiber  is  better  seen  with  the  high  power  (240  diameters), 
while  Cohnheim's  fields  (Fig.  55)  can  only  be  seen  in  transverse  micro- 
tome sections.  Muscle-spindles  are  easily  found  in  transverse  sections  of 
the  human  omo-hyoid  muscle. 

No.  69. — Tendons. — Cut  from  a  tendon  a  piece  5  or  10  cm.  long, 
and  let  it  dry  in  the  air  (but  not  in  the  sun).  Thin  tendons  {e.  g., 
that  of  the  flexor  digitorum  pedis)  at  room- temperature  are  sufficiently 
dry  in  twenty-four  hours.  Thicker  tendons  require  several  days.  With 
the  scalpel  (not  the  razor)  make  a  smooth  transverse  surface  and  then 
cut  thin  shavings  from  the  tendon,  supporting  it  on  the  thumb  of  the 
right  hand  and  with  the  remaining  fingers  grasping  the  scalpel  (the  man- 
ipulation is  the  same  as  in  sharpening  a  pencil).  Throw  the  shavings 
into  a  capsule  containing  distilled  water  and  in  two  minutes  examine 
in  a  drop  of  the  same  medium  (Fig.  112).  To  preserve,  stain  in  3  c.c.  ot 
picrocarmine  for  five  minutes  and  mount  in  dilute  glycerol.  Very  fre- 
quently a  streak  is  seen  extending  across  the  entire  section  ;  this  is 
produced  by  the  knife. 

Place  another  section,  unstained,  in  a  drop  of  water  on  a  slide  ; 
treat  it  under  the  cover-glass  with  a  drop  of  acetic  acid  ;  the  edges  of 
the  section  soon  exhibit  swollen  convoluted  bands  (acetic  acid  reaction 
of  connective  tissue,  p.  89). 

No.  70. — For  the  study  of  the  minute  stntcture  of  tendon,  its  cells 
and  their  processes,  place  a  thin  tendon,  as  fresh  as  possible  {e.  g.  that  of 
the  palmaris  longus  muscle),  in  pieces  3  cm.  long  in  100  c.c.  of  0.5  per 
cent,  chromic  acid  (p.  21)  for  at  least  four  weeks.  The  chromic  acid 
should  be  changed  several  times  during  this  period.  Then  wash  the 
tissue  in  running  water  one  or  two  hours  and  harden  it  in  about  40  c.c. 
of  gradually  strengthened  alcohols  (p.  35).  The  sections  should  be  cut 
with  a  very  sharp  razor  ;  often  the  tendon  is  so  brittle  that  it  falls  to 
pieces  in  cutting.  The  sections  need  not  be  very  thin.  Mount  them 
unstained  in  diluted  glycerol.  Examined  with  the  low  power  and  direct 
light  (with  the  mirror  muffled)  they  yield  beautiful  pictures,  better  than 
the  preparations  made  like  technic  No.  69. 

No.  71. — Tendon-cells. — From  the  tail  of  a  rat  or  a  mouse  cut 
pieces  of  tendon  0.5  to  i  cm.  long  and  place  them  in  5  c.c.  of  alum- 
carmine.     The  following  day  (or  later)  transfer  the  swollen  pieces  to  a 


THE    NERVOUS    SYSTEM.  1 8/ 

dry  slide  and  rapidly  tease  them  (p.  29).  It  is  not  necessary  to  separate 
the  tendon  into  very  small  bundles,  but  care  should  be  taken  that  the 
bundles  lie  straight.  Then  cover  the  preparation  with  a  drop  of  distilled 
water  and  a  cover-glass.  With  the  low  power  the  rows  of  cells  appear 
for  the  most  part  as  dark  streaks  ;  these  are  the  cell-nuclei  seen  in  pro- 
file. In  surface  views  the  nuclei  appear  dull  red.  The  body  of  the 
cells,  the  protoplasm,  can  only  be  seen  with  the  high  power  ;  viewed 
laterally,  it  appears  as  a  sharp,  dark  streak  (Fig.  113  a)  ;  from  the  sur- 
face, paler  and  delicate  (Fig.  113  b).  Not  infrequently  the  cells  are 
indented,  so  that  they  are  visible  partly  from  the  edge  and  partly  from  the 
surface.  Occasionally  the  connective-tissue  fibers  can  be  distinguished 
as  delicate  parallel  lines  ;  the  fine  elastic  fibers  with  their  sharp  contours 
are  always  distinct.  The  focus  should  be  changed  by  means  of  the 
micrometer-screw  and  the  different  planes  of  the  section  examined.  If 
the  cells  are  not  distinct  add  a  drop  of  acetic  acid  (p.  53).  To  preserv^e, 
displace  the  water  with  diluted  glycerol  (p.  23). 

No.  72. — Muscle  ami  tendon. — Remove  the  skin  from  the  hind  leg 
of  a  frog  just  killed  and  with  scissors  cut  off  the  leg  above  the  knee- 
joint,  just  above  the  origin  of  the  gastrocnemius.  Fix  it  in  50  c.c.  of 
Zenker's  fluid  (p.  ^-x,)  and  harden  in  gradually  strengthened  alcohols 
(P-  35)-  Cut  off  the  muscle  with  a  piece  of  the  tendo-Achillis  and  stain 
it  in  bulk  in  borax-carmine  (p.  40).  Then  harden  again  in  90  per  cent, 
alcohol.  Cut  sagittal  longitudinal  sections,  placing  the  edge  of  the  razor 
on  the  tendon  situated  on  the  posterior  surface  of  the  muscle.  Mount 
in  xylol-balsam  (Fig.  114). 


IV.  ORGANS  OF  THE  NERVOUS  SYSTEM. 
I.  THE  CENTRAL  NERVOUS  SYSTEM.* 

The  Spinal  Cord. 

Topography. — The  spinal  cord  consists  of  a  white  and  a  gray  sub- 
stance, distinguishable  by  the  unaided  eye.  The  arrangement  and 
relation  of  these  two  substances  are  best  recognized  in  cross-sections  of 
the  spinal  cord. 

The  tuhite  substance  encircles  the  gray  substance  and  is  partially 
divided  by  a  deep  anterior  cleft,  the  anterior  median  fissure,  and  a  poste- 

*  I  shall  confine  myself  here  to  a  brief  account  of  the  topography  and  of  the  histology 
of  the  spinal  cord  and  the  brain.  An  exhaustive  presentation  of  the  architecture  of  the  central 
nervous  system,  the  paths  of  the  nerve-fibers,  and  the  complicated  structures  in  connection  with 
the  "nuclei  "  of  the  cranial  nerves  in  the  oblongata  would  exceed  the  limits  of  this  "  Histol- 
ogy." The  student  is  referred  to  special  text-books,  of  which  Edinger's  "  Vorlesungen  iiber  den 
Bau  der  nervosen  Centralorgane,"  Barker's  "  Nervous  System  and  its  Constituent  Neurones," 
and  Van  Gehuchten's  "Anatomie  du  systeme  nerveux  de  Fhomme  "  are  recommended. 


158  HISTOLOGY. 

rior  septum  (formerly  called  the  posterior  median  fissure)  into  a  right  and 
a  left  half.  Each  half  is  subdivided  by  the  furrows  marking  the  exit  of 
the  anterior  and  the  posterior  roots  of  the  spinal  nerves  into  a  large  lat- 
eral cohiinn,  an  anterior  coliunn,  and  a  posterior  column.  In  the  lower 
cervical  and  the  upper  thoracic  region  of  the  spinal  cord  two  parts  can 
be  distinguished  in  each  posterior  column,  of  which  the  median  is  named 


Zona 
tertninalis.  --^ 


Entrance  zone. 


Posterior  Median  "l  Portion  of 

median       Posterior      I  >  posterior 

septum.        column.      |  Lateral)    root. 


Posterior  root-bundle. 


Zona_ 
spongiosa. 


'O   •- 


Substantia__.    -iff^-^i 
gelatinosa.  "  -^ 


Formatio 
reticularis 


Posterior  horn. 


jA  _^ Pia  mater. 


Horn 
spongi- 


.^j.  ;~~-- Lateral 

;^7i  column. 


Laterals 
posterior, 


\:*i. 


■iiy 


Medial  anterior    ^  ^j"*?!^^    . 
Group  of  nerve-cells.  ■"/' 


-^'um 


^^  \ 


Anterior  horn. 


Central  canal. 


Anterior  root-        White     Anterior  median     Anterior  column, 
bundle.        commissure.        fissure. 

Fig.  115. — Cross-section  of  the  Lumbar  Enlargement  of  the  Human  Spinal  Cord.      X  8. 

Technic  No.  74. 


the  column  of  Goll  (funiculus  gracilis)  and  the  lateral  the  column  of  Bur- 
dacli  (funiculus  cuneatus).  The  anterior  columns  are  united  by  the 
white  commissure  at  the  bottom  of  the  anterior  median  fissure. 

The  gray  substance  in  cross-section  appears  in  the  form  of  an  H 
and  in  its  entirety  consists  of  two  lateral  columns  which  are  connected 
by  a  frontally  situated  lamella,  the  gray  commissure.  On  each  column  a 
thick  anterior  Jiorn  and  a  slender  posterior  Jiorn  can  be  distinguished. 


THE    NERVOUS    SYSTEM. 


189 


At  the  lateral  portion  of  the  anterior  horns,  in  the  same  frontal  plane 
with  the  central  canal,  are  the  lateral  horns,  which  are  especially  well 
developed  in  the  upper  thoracic  region.  From  the  anterior  circum- 
ference of  the  anterior  horns  the  anterior  roots  of  the  spinal  nerves 
emerge  in  several  bundles,  while  the  posterior  roots  enter  at  the  posterior 
and  median  side  of  the  posterior  horns.  Laterally,  at  the  base  of  each 
posterior  horn  a  net-like  mass  of  trabecular  of  gray  substance,  the 
reticular  process  (formatio  reticularis)  is  found  ;  at  the  median  side  of 
each  posterior  horn,  near  the  gray  commissure,  lies  the  column  of  Clarke 
(dorsal  nucleus),  visible  as  a  well-defined  group  in  the  whole  length  of 
the  thoracic  and  in  the  upper  part  of  the  lumbar  region  and  not  entirely 
absent  in  the  remaining  portions  of  the  cord.  At  the  summit  of  the 
posterior  horns  a  glistening,  jelly-like  mass,  macroscopically  easily 
perceptible,  the  substantia  gelatinosa  (^Rolando),  can  be  distinguished. 
Dorsalward  to  this  is  the  small  so7ia  spongiosa,  at  the  dorsal  edge  of 
which  is  found  the  border-zone,  zona  terniinalis,  an  area  of  cross - 
sectioned  thin  nerve-fibers.  In  the  gray  commissure  lies  the  cross- 
section  of  the  central  canal,  which  extends  through  the  whole  length  of 
the  spinal  cord  and  is  surrounded  by  the  substantia  grisca  centralis, 
diminishing  in  mass  caudahvard.  T\\q  central  canal  \s,  from  0.5  to  i  mm. 
in  diameter  ;  not  infrequently  it  is  obliterated.  The  divisions  of  the 
gray  commissure  in  front  of  and  behind  the  central  canal  are  respec- 
tively named  the  anterior  and  the  posterior  gray  commissure.  In  man  the 
latter  is  the  smaller.  From  the  entire  periphery  of  the  gray  substance 
coarser  or  finer  processes,  the  septula  medullaria  radiate  into  the  white 
substance.  In  the  cervical  and  lumbar  enlargements  of  the  spinal  cord 
the  gray  matter  is  more  powerfully  developed  than  in  the  thoracic  re- 
gion ;  there  is  a  corresponding  variation  in  the  form  of  the  H-  The 
end  of  the  conus  medidlaris  consists  almost  wholly  of  gray  substance. 

Minute  structure. — The  gray  substance  must  be  first  considered,  a 
knowledge  of  its  composition  being  essential  to  the  comprehension  of 
the  structure  of  the  white  substance.  The  gray  substance  consists  of 
multipolar  nerve-  (ganglion)  cells,  that  with  their  dendrites  and  nerve- 
processes  form  a  dense  nervous  tangle,  the  "  nerve-felt  "  {iieuropileni). 
This  felt  is  penetrated  by  nerve-fibers,  coming  partly  from  the  white 
columns,  partly  from  the  posterior  roots  ;  the  whole  is  supported  by  a 
framework  of  neuroglia. 

We  have  therefore  to  consider  first  the  nerve-cells,  then  the  nerve- 
fibers  ;  the  neuroglia,  which  also  occurs  in  the  white  substance,  shall  be 
described  at  the  conclusion  of  the  entire  recital. 

I.   The  nerve-cells,  in  accordance  with  the  relations  and  distribution 


190 


HISTOLOGY. 


of  their  nerve-process,  are  divided  into  (i)  motor  cells,  (2)  column  cells, 
and  (3)  internal  cells.* 

The  motor  nervc-cclh  {I'hizonciirons,  Fig.  1 16)  lie  in  two  groups  f  in 
each  anterior  horn.  They  possess  a  large  cell-body  (67  to  135  //)  and 
long  dendrites,  extending  far  into  the  neighborhood  ;  their  nerve-process 


Fig.  116. 


-Two  Forms  of  Motor  Nerve-cells  from  the  Anterior  Horn  of  the  Spinal  Cord  of  a 
Rabbit,     n.  Nerve-process.     X  60.     Technic  No.  76.     (Schaper.) 


'^  Editor'' s  remark;  A  classification  and  nomenclature  based  upon  the  behavior  and 
distribution  of  the  axis-cylinder  have  recently  been  suggested  in  America  that  in  many  respects 
appear  to  me  to  be  appropriate  and  natural,  and  they  have  been  widely  accepted.  According  to 
this  two  chief  groups  are  distinguished,  namely :    I,  axoneiirons,  and,  II,  ganglioneurons. 

I.  The  axoneurons  embrace  all  those  neurons  the  cell-body  (nerve-cell)  of  which  lies 
in  the  interior  of  the  spinal  cord  or  the  brain.  Corresponding  to  the  different  behavior  of  the 
nerve-process  they  are  further  divided  into  two  subordinate  groups,  namely  : 

(rt)  Rhizoneurons,  the  nerve-process  of  which  leaves  the  spinal  cord  through  the  anterior 
root  (they  comprise  the  motor  nerve-cells),  and — 

(b)  Endaxonetcrons,  the  nerve-process  of  which  does  not  leave  the  spinal  cord.  Among 
these  we  may  distinguish  (i)  those  the  nerve-process  of  which  enters  the  different  columns  of 
the  white  substance  [column  cells),  and  (2)  those  the  nerve-process  of  which  within  the  gray 
substance  rapidly  breaks  up  into  its  terminal  ramifications  {internal  cells). 

II.  The  ganglioneurons  represent  those  neurons  the  cell-body  of  which  lies  within  the 
spinal  ganglia  or  the  cerebral  ganglia  and  that  stand  in  connection  with  the  central  nervous  sys- 
tem only  by  means  of  their  central  process. 

I  A  medial-anterior  and  a  lateral-posterior  group,  separate  in  the  cervical  and  lumbar  en- 
largements {cf.  Fig.  115),  but  in  the  uppermost  cervical  and  in  the  thoracic  region  united  in  a 
single  colony.  In  longitudinal  sections  it  may  be  seen  (conspicuously  in  amphibians)  that  the 
cell  groups  have  a  segmental  arrangement  corresponding  to  the  original  territory  of  the  indi- 
vidual roots. 


THE    NERVOUS    SYSTEM. 


191 


emerges  from  the  summit  of  the  anterior  horn,  makes  an  obHque  descent 
through  the  white  substance,  at  the  same  time  receives  a  medullary 
sheath  and  becomes  the  axis-cylinder  of  a  medullated  nerve-fiber. 
Occasionally  the  axis-cylinder  process  gives  off  a  few  insignificant  lateral 
twigs  (collaterals)  before  leaving  the  gray  matter.  It  leaves  as  a  con- 
stituent part  of  an  anterior  (ventral)  root-fiber  bundle  of  the  spinal  cord. 
All  anterior  root-fibers  arise  from  the  motor  cells  of  the  anterior  horns, 
from  those  of  the  same,  not  the  opposite  side  (Fig.  1 17). 

The  cobiinn  cells  iStrangzcllen^  endaxoneiirons)  constitute  the  chief 
mass  of  the  nerve-cells  of  the  gray  substance  and  lie  everywhere  in  it 
(except  in  the  places  occupied  by  the  motor  nerve-cells),  partly  scattered, 
partly  in  groups  in  the  lateral  horn  and  in  the  dorsal  nucleus  (Fig.  1 17). 


Posterior  root. 


Lateral  column  cell 
with 

Nerve-process.    ' 
Gray  substance. 

White  substance.  _  . 


Central  canal. 


Motor  cell  of  the  latera 
posterior  group. 


Commissure  cell. 


Nerve-processes. 


Fig.  117.— Cross  section  of  the  Spinal  Cord  of  a  Seven-day-old  Embryo  Chick.    X  80.    The  white 
substance  is  but  slightly  developed,  the  central  canal  is  still  very  large.    Technic  No.  76. 


They  are  mostly  smaller  than  the  motor  nerve-cells  and  possess  few, 
little-branched,  but  far-reaching  dendrites.  Their  nerve-process,  after 
sending  off  numerous  collaterals  in  the  gray  substance,  enters  the  white 
substance — in  the  anterior  or  lateral  column,  very  rarely  the  posterior 
column — either  on  the  same  or  on  the  opposite  side.  Cells  of  the 
latter  kind  are  also  named  commissure  cells, '^^  because  the  nerve -process 
passes  through  the  anterior  gray  commissure  before  entering  the  white 
substance.      Having  arrived  in  the  white  substance  the  nerve-process  of 


*  The  commissure  cells  occupy  an  area  which,  arch-like,  embraces  the  central  canal  on 
the  ventral  side  ;  here  they  are  of  conspicuous  size,  approaching  that  of  the  motor  cells  of  the 
anterior  horns.  Also  farther  back,  in  the  median  division  of  the  gray  substance,  scattered  com- 
missure cells  occur,  but  they  are  wanting  in  the  posterior  horns. 


192 


HISTOLOGY. 


the  majority  of  the  column  cells  *  divides  into  a  vertical  ascending  and 
descending  "  stem-fiber,  "  that  in  its  course  parallel  to  the  longitudinal 
axis  of  the  spinal  cord  sends  off  lateral  twigs  (collaterals),  which  return 
to  the  gray  substance,  where  they  branch  and  terminate  in  free  fibrils  ; 
the  stem-fibers  themselves  finally  terminate  like  the  collaterals.  The 
collaterals  that  enter  from  the  anterior  columns  penetrate  the  anterior 
horns  singly  or  in  bundles,  where  they  weave  themselves  about  the  large 


Motor  cell. 


Commissure  cell. 


Column  cell.     t (r 


Internal  cell. 


Collaterals. 


Ascending  stem-fiber. 


Spinal  ganglion  cell. 


Descending  stem-fiber. 


Fig.  118.— Scheme  of  the  Location  and  Ramification  of  the  Nerve-cells  and  of  the  Posterior 
Nerve-roots  of  the  Spinal  Cord. 

motor  cells  ;  they  are  especially  numerous  in  the  antero-lateral  region  of 
the  anterior  horns  ;  not  less  numerous  are  the  collaterals  coming  from 
the  lateral  columns.     The  spindle-shaped  "  marginal  cells  "  lying  in  the 


*  Excepting  the  nerve-processes  coming  from  the  dorsal  nucleus,  which  turn  cranialward 
and  proceed  to  the  cerebellum.  The  nerve-processes  of  still  other  column  cells  enter  the  white 
substance  and  there,  wi^Aozii  dividing,  turn  upward  or  downward.  Under  the  name  of  "pluri- 
funicular  cells"  column  cells  have  been  described,  the  nerve-process  of  which  divides  in  the 
gray  substance  into  two  or  three  branches  and  continues  in  as  many  fibers  in  different  columns. 


THE    NERVOUS    SYSTEM. 


193 


zona  spongiosa  (p.  189)  also  belong  to  the  column  cells.  In  the  adult 
the  nerve-processes  of  all  the  column  cells  are  enveloped  in  a  medullary 
sheath. 

The  cells  so  far  described  belong  to  the  type  with  the  long  ner\'e- 
process  (p.  117).  There  is  another,  transitional,  variety  of  cell,  the 
nerv^e-process  of  which  rapidly  divides  and  remains  within  the  gray  sub- 
stance. Because  they  do  not  pass  beyond  the  gray  substance  these 
elements  are  named — 

Litertial  cells;  they  occur  in  the  posterior  horns  (Fig.  118), 
where  their  terminal  ramification  spreads  out  either  on  the  same  or  on 
the  opposite  half  of  the  spinal  cord. 

2.  The  nen'C-fibcrs,  that  enter  the  gray  substance  from  the  anterior  and 
lateral  columns,  partly  arise  from  the 
medullated  collaterals  and  terminals 
of  the  nerve-processes  of  the  column 
cells,  partly  from  the  nerve-processes 
(likewise  invested  by  a  medullary 
sheath)  that  come  from  the  brain.* 
In  addition  there  are  the  medullated 
nerve-fibers  of  the  posterior  (dorsal) 
roots,  which  originate  in  the  centrip- 
etal processes  of  the  cells  of  the 
spinal  ganglia  (p.  215).  These  pos- 
terior root-fibers  enter  the  spinal 
cord  in  two  groups,  a  lateral,  which 
runs  in  the  zona  terminalis,  and  a 
larger  median,  which  runs  in  the 
posterior  column.  These  fibers  do  not  directly  enter  the  gra}-  sub- 
stance, but  each  divides  Y-shape  into  a  longer  ascending  and  a  shorter 
descending  stem-fiber  (Fig.  119),  from  which  numerous  collaterals 
diverge  at  right  angles  (Fig.  1 18).  These  now  enter  the  gray  substancef 
and  with  their  terminal  fibrils  distribute  themselves  over  nearly  every 
point  of  the  same.  One  set  terminates  principally  in  the  summit  of  the 
posterior  horn  ;  these  fibers  take  their  origin  in  the  lateral  root-fiber 
group  and  form  a  very  fine-fibered,  dense  plexus,  that  also  partly  lies 
in  the  substantia  gelatinosa  (Fig.   120,  <r);'a  second  set  terminates  in  the 


Ascending  stem-fiber. 


Descending  stem-fiber.   — 


Nerve-fibers  of  the 
posterior  root. 


Fig.  119. — From  a  Longitudinal  Section  of 
THE  Spinal  Cord  of  a  Newborn  Rat.  >,  no. 
The  section  shows  two  posterior  nerve-roots. 
The  collaterals  are  not  visible.  Technic  No.  76. 


*  For  an  account  of  the  exact  course  of  these  fibers  the  student  is  referred  to  special  text- 
books. 

t  An  exception  occurs  in  the  case  of  some  fiber-bundles  which  directly  enter  into  the 
gelatinous  substance  and  partly  in  this  or  ventral  thereto  (in  the  territory  of  the  posterior  horn) 
divide  into  ascendintj  and  descendins;  stem-fibers. 


194 


HISTOLOGY. 


dorsal  nucleus  (Fig.  120,  «)  ;  *  these  originate  in  the  median  root-fiber 
group,  as  also  a  third  set  which,  penetrating  the  median  portion  of 
the  substantia  gelatinosa,  passes  ventralward  into  the  anterior  horn  and 
there,  radiating  fan-shape,  surrounds  the  motor  nerve-cells  (Fig.  120,  b) ; 
these  latter  very  robust  collaterals  ("  reflex  collaterals  ")  arise  from  the 
proximal  portions  of  the  stem-fibers,  next  to  the  point  of  bifurcation, 
and  form  the  reflex  bundle. f  A  fourth,  smaller  set  of  collaterals  passes 
through  the  posterior  gray  commissure  to  the  posterior  horn  of  the  oppo- 
site side.  A  fifth,  likewise  lesser  set  crosses  transversely  through  the 
base    of    the    posterior    horns    to    the    lateral     column.       The     stem- 


Glia- 


Anterior 
horn. 


Blood-vessels. 


Collateral  of  a  column  cell. 


Fig.  120.— Cross-section  of  the  Spinal  Cord  of  a  Newborn  Rat,  showing  Collateral  Fibers. 
X  75.     In  the  right  half  only  one  representative  of  each  variety  has  been  sketched.     Technic  No.  76. 

fibers,  probably  not  until  after  a  long  course,  sometimes  extending  into 
the  oblongata,  turn  into  the  gray  substance,  where  they  terminate  like  the 
collaterals. 

The  peculiarities  of  the  substantia  grisea  centralis  and  substantia 
gelatinosa,  which  belong  to  the  gray  substance,  are  dependent  upon  the 
abundance  of  the  neuroglia  and  shall  be  described  with  this. 

*  Here  the  medullary  siieaths  extend  farther  than  elsewhere — that  is,  to  the  last  terminal 
ramifications. 

f  The  reflex  bundle  and  the  collaterals  of  the  dorsal  nucleus  sink  into  the  gray  substance 
in  an  arch  with  the  concavity  lateralward  and  form  a  conspicuous  mass  easily  perceived  (Fig. 
115).      The  place  at  which  they  enter  the  gray  substance  has  been  named  "root-entrance  zone."' 


THE    NERVOUS    SYSTEM.  I95 

The  luJiite  sitbstaiice  consists  exclusively  of  nerve-fibers,  medullated, 
that  do  not  possess  a  neurilemma  (p.  120),  and  nonmeduUated.  The  fibers 
difler  greatly  in  thickness  ;  the  thickest  are  found  in  the  anterior  columns 
and  in  the  lateral  parts  of  the  posterior  columns,  the  thinnest  in  the  median 
parts  of  the  posterior  columns  and  in  the  lateral  columns  where  the  white 
substance  touches  the  gray.  In  the  remaining  portions  thick  and  thin  fibers 
are  intermingled.  The  majority  of  the  nerve-fibers  run  parallel  with  the 
long  axis  of  the  spinal  cord,  hence  in  cross-sections  are  cut  transversely. 
In  addition  there  are  fibers  that  take  an  oblique  direction  ;  these  are 
found  in  large  numbers  in  front  of  the  gray  commissure,  where  they 
cross  and  form  the  white  commissure  (Fig.  1 1  5). 

An  attempt  to  classify  the  nerve -fibers  according  to  their  origin  will 
result  as  follows  :  i,  fibers  which  are  processes  of  the  posterior  roots  ; 
the  entire  posterior  columns  consist  of  posterior  root-fibers,  because  the 
latter  (or  their  stem-fibers),  entering  in  the  lumbar  region  of  the  spinal 
cord,  are  pushed  toward  the  median  line  by  the  fibers  entering  at 
higher  levels  ;  2,  fibers  which  are  processes  of  the  column  cells  (Fig. 
118  and  120);  3,  fibers  which  are  processes  of  the  nerve-cells  of 
the  brain.  The  latter  two  occupy  the  anterior  and  lateral  columns  and  do 
not  run  an  interlacing,  irregular  course,  but  are  united  in  compact  bundles. 

The  supportijig  franieivork  of  the  spinal  cord  is  constructed  of  two 
genetically  distinct  formations  :  i,  connective-tissue  extensions  of  the  pia, 
which  penetrate  the  white  substance  as  sheaths  for  the  blood-vessels  ; 
this  connective-tissue  framework  grows  steadily  thinner  as  it  approaches 
the  gray  substance,  into  which  it  does  not  extend  ;  2,  the  neuroglia 
("  nerve-cement  "),  which  is  derived  from  the  same  embryonal  anlage  as 
the  central  nervous  system.  The  neuroglia  principally  consists  of 
nucleated  elements,  the  glia-cells  (Fig.  1 21),  and  (perhaps)  of  a  small 
amount  of  homogeneous  ground  substance.  There  are  two  kinds  of 
glia-cells:  i.  The  ependymal  cells,  which  in  a  single  layer  hne  the 
lumen  of  the  central  canal.  In  youth  they  are  beset  with  cilia, 
their  cylindrical  body  is  prolonged  in  an  extended  process  (Fig. 
121),  that  in  the  embryo  reaches  to  the  surface  of  the  spinal  cord, 
where  it  terminates  in  a  simple  or  branched  end.  The  cells  of 
the  ependyma  are  phylogenetically  the  older ;  they  arise  also  onto- 
genetically  first,  but  in  the  further  course  of  development  undergo 
regression  in  different  degrees  ;  the  long  processes  in  particular  are  in- 
volved, which  retain  their  original  length  to  the  surface  of  the  spinal 
cord  only  in  the  region  of  the  posterior  median  septum  *   and  opposite, 

*  The  posterior  median  septum  consists  for  the  greater  part  of  processes  of  ependymal 
cells. 


196 


HISTOLOGY. 


to  the  base  of  the  anterior  median  fissure.  In  the  course  of  devel- 
opment one  division  of  the  ependymal  cells  wanders  periphery  ward  and 
becomes  transformed  into  astrocytes.  Not  infrequently  the  central  canal 
is  completely  obliterated.  2.  The  astrocytes  (Deiters's  cells),  in  the  be- 
ginning of  their  development,  all  lie  in  the  gray  substance  ;  later  some 
retreat  into  the  white  substance  and  then  are  very  differently  shaped. 
Of  the  numerous  processes  of  the  astrocytes  one,  the  "  chief  process  " 
(Fig.  121),  frequently  originates  earliest,  the  others,  partly  finer  and 
partly  coarser  "secondary"  processes,  arise  later.  Many  of  these  cells 
reach 'with  much-branched  processes  to  the  surface  of  the  spinal  cord, 


From  the  substantia  gelatinosa  of  a  newborn  rat. 

Glia-cell. 


Central  canal. 


Ependymal  cells. 


Concentric  glia-cells  from  a  six- 
week-old  cat. 


Glia-cell  of  the  gray  substance  of  the  base  of  the 
posterior  horn  of  a  human  embryo. 


Fig.  121.— Glia-cells  from  the  Spinal  Cord.     X  280.     Technic  No.  76. 


where  they  terminate  in  expanded  ends  *  and  form  a  conspicuous  bor- 
der, the  superficial  gUa-zone  ("gelatinous  cortical  layer"  or  "  horn- 
spongiosa").  Of  the  developed  cells  two  varieties,  united  by  transi- 
tional forms,  are  distinguished  :  {a)  The  short-rayed  cells  (mossy-cells) 
possess  shorter,  very  richly  branched  processes,  that  not  infrequently  are 
attached  to  the  blood-vessels  ;  they  chiefly  occur  in  the  gray  substance. 
(J))  The  long-rayed  cells  (spider-cells),  the  more  usual  form,  have  a  small 

*  These  expanded  ends  stand  close  beside  one  another  and  form  a  "  membrana  limitans 
meningea,"  which  is  not  an  independent  membrane  any  more  than  the  internal  limiting  mem- 
brane of  the  retina  fsee  The  Visual  Organ). 


THE    NERVOUS    SYSTEM. 


197 


White 

substance. 

Horn-spongiosa. 

/^M.    «      , '  ■ 

'••  ■   ---^:.., 

Cross-sections  of  medul- 
lated   nerve-fibers  con- 
sisting of— 

-^'J:-:::-. 

;  *  » •   'v 

Axis-cylinder 

■*-./,         •     'e 

•v'^       "'-^.^ 

and 

•    '.'    -"         'l'- 

.' '  -•■.               \ 

Medullarj-  sheath. 

cell-body,  from  which  besides  short,  also  many  longer,  rigid,  less- 
branched  processes  radiate  (Fig.  121) ;  these  chiefly  occur  in  the  white 
substance  and  are  not  apt  to  be  confused  with  the  ganglion  cells. 
By  the  interlacing  of  the  numerous  fine  processes  of  neighboring  glia- 
cells  (they  do  not  anasto- 
mose) a  close  web  is  con- 
structed which  envelops 
each  individual  nerve- 
fiber.* 

In  the  substantia  gri- 
sea  centralis  and  substantia 
gelatinosa  the  neuroglia  as- 
sumes a  totally  different  ap- 
pearance. In  the  former 
the  astrocytes  with  their 
here  very  long,  stiff,  un- 
branched  processes  are  con- 
centrically arranged  in  a 
close  fiber-wreath  (Fig. 
121).  These  and  the  cells 
of  ependyma  are  together 
called  "  central  ependyma 
filaments."  The  substantia 
gelatinosa  consists  of  a  small  number  of  very  small  ganglion  cells,  the 
nerve-processes  of  which  turn  into  the  zona  terminalis,  of  a  plexus  of 
delicate  nerve-fibrils,  and  of  nerve-fibers  (collaterals)  passing  through  ; 
there  is  besides  a  granular  substance  present  which  has  arisen  by  a 
transformation  of  numerous  and  very  delicate  processes  of  the  few  astro- 
cytes occurring  there  (Fig.  121). 

The  Braix. 

The  brain,  like  the  spinal  cord,  is  composed  of  a  white  and  a  gray 
substance,  which  in  their  minute  structure  agree  on  the  whole  with  the 
same  substances  in  the  cord.  But  the  arrangement  of  the  two  substances 
in  the  brain  is  a  much  more  diversified  one  than  in  the  spinal  cord. 


Glia-cells. 


"^^— ■"-'»^    Connective  tissue. 


Blood-vessels. 


Fig.  122.— From  a  Cross-section  of  the  Human  Spinal 
Cord  in  the  Region  of  the  Lateral  Column.  X  i8o. 
Technic  No.  75. 


*  In  accordance  with  this  account  the  neuroglia  consists  of  cells  and  their  processes 
only  ;  whether  also  free  tibers  occur,  that  have  become  detached  from  the  cell-body,  has  not 
yet  with  certainty  been  distinguished.  The  fact  that  a  portion  of  the  delicate  processes 
(fibers)  are  differentiated  by  their  chemical  nature  from  the  usual  cell-processes  does  not  prove 
that  fibers  and  cells  are  entirelv  distinct  structures. 


198  HISTOLOGY. 

The  gray  substance  of  the  brain  occurs  in  four  aggregations  : 

(a)  As  the  cerebral  cortex,  an  expansion  covering  the  entire  surface 
of  the  cerebral  hemispheres. 

{b')  In  the  form  of  discrete  masses,  which  are  situated  in  the  cere- 
bral ganglia, — the  corpora  striata,  the  optic  thalami,  the  corpora  quad- 
rigemina. 

{c)  As  the  lining- of  the  ventricles,  which  is  the  direct  continuation 
of  the  gray  substance  of  the  spinal  cord. 

id)  As  the  cerebellar  cortex,  an  expansion  covering  the  surface  of 
the  cerebellum.  Discrete  masses  also  occur  in  the  interior  of  the  cere- 
bellum. 

All  these  aggregations  have  numerous  connections  with  one  an- 
other by  means  of  fiber-tracts  of  white  substance. 

THE  CEREBRAL  CORTEX. 

In  vertical  sections  of  the  cerebral  cortex  four  zones,  not  sharply  de- 
fined from  one  another,  are  distinguished. 

1.  The  violecidar  zone  (neuroglia  layer),  the  most  superficial,  in 
ordinary  preparations  appears  finely  granulated  or  reticulated  and  con- 
tains, besides  many  glia-cells,  an  interlacement  of  medullated  nerve-fibers 
running  horizontally,  the  tangential  fibers  (Fig.  123).  By  means  of 
Golgi's  method  it  may  be  seen  that  the  reticulum  is  partly  formed  by  the 
dendrites  of  the  pyramidal  cells  of  the  second  and  third  zones  (see  sub 
2  and  3),  and  partly  by  the  processes  of  glia-cells.  Besides  the  latter 
the  cells  of  Cajal  occur  in  the  molecular  zone  ;  they  possess  an  irregu- 
larly shaped  cell-body  that  sends  out  very  long  processes  running  par- 
allel to  the  surface,  from  one  portion  of  which  vertically  to  the  surface 
ascending  lateral  twigs  arise  *  (Fig.  124,  i). 

2.  The  sone  of  the  small  pyramidal  cells  (Fig.  123,  Fig.  124)  is 
characterized  by  ganglion  cells  from  10  to  12//  in  size  and  of  a  pyram- 
idal form  ;  the  apex  of  the  pyramidal  cell  is  prolonged  into  a  long 
ramifying  protoplasmic  process  (dendrites), f  that  after  giving  off  minute 
lateral  twigs  enters  the  molecular  zone,  where  it  terminates  in  numerous, 
often  serrulate  branches  (Fig.  124,  2)  ;  only  small  dendrites  spring  from 

*  In  animals  four  and  even  more  "  nerve-processes  "  of  Cajal' s  cells  have  been  described. 
It  seems  as  if  different  unrelated  cell  forms  were  grouped  under  this  name.  In  the  forms  de- 
scribed as  Cajal's  cells  in  man  a  true  nerve-process  has  not  been  distinguished;  it  is  probable 
that  these  latter  elements  are  glia-cells. 

f  For  this  reason  it  is  difficult  to  determine  the  size  of  the  pyramidal  cells  ;  the  consider- 
able differences  in  the  estimated  size  may  be  referred  to  this  gradual  passage  of  the  cell-body 
into  the  apical  process. 


Superradial 
reticulum. 


Stripe  of 
Gennari. 


1  f-*  »'r^i7^'^^tf:sy 


/^ 


1/  \,     '^   '■  '4:^:4 


/'i!/ 


/ 


Medulla. 


.?^ 


^ 


Fig.  123.— \'ertical  Section  of  Human  Cerebral 
Cortex.    X  60.    Technic  No.  77. 


199 


■|G.     124.— SCHK.ME     OF    THF.     CEREBRAL     CoRTEX,    sketched 

from  specimens  prepared  according  to  Technic  No.  79  b. 
I.  Cell  of  Cajal  (glia-cell?).  2,  2'.  Small  pyramidal  cells. 
3.  Large  pyramidalcell.  4.  Polymorphous  cell.  5,  5'.  Cells 
of  Golgi's  type.  6.  Ner\e-fiber  ending  in  the  superficial 
zone:  a,  mossy-cell,  b,  spider-cell  (glia-cells).  The  epen- 
dymal  cells  are  not  represented. 


200 


HISTOLOGY. 


the  lateral  surfaces  and  the  base  of  the  cell.  The  nerve-process  always 
arises  from  the  base  and  after  giving  off  branched  collaterals,  as  a  rule, 
passes  toward  the  white  substance,  there  to  become  the  axis-cylinder  of 
one  or,  by  division,  of  two  nerve-fibers  ;  occasionally  it  turns  and  runs 
to  the  molecular  layer,  where  it  divides  and  enters  the  web  formed  by 
the  tangential  fibers  (Fig.  124,  2').  The  nerve-process  and  the  collater- 
als are  enveloped  in  a  meduUated  sheath. 

3.  The  zone  of  the  large  pyramidal  ccllsxs  distinguished  from  the  pre- 
ceding zone  'by  the  greater  size  of  its  elements  (from  20  to  30  (j.,  the  so- 
called  giant  pyramidal  cells  in  the  anterior  central  convolution  even 
measure  as  much  as   80 /jt);  the  extremely  robust   nerve-process,  after 

giving  off  several  collaterals  in  the  gray  cor- 
tex, always  goes  to  the  white  substance  (Fig. 

124,  3)- 

4.  In  the  zone  of  the  polymorphous  nerve- 
cells  the  majority  of  the  elements  are  oval  or 
polygonal  ;  an  apical  dendrite  is  wanting  ;  the 
delicate  nerve-process  after  sending  off  a  num- 
ber of  collaterals  enters  the  white  substance, 
where  it  passes  into  one,  or  dividing  into 
T-branches,  into  two  nerve-fibers  (Fig.  124,  4). 

In  the  last  three  zones  gangUon  cells  of 
Golgi's  type  also  are  found  (p.  118).  Their 
branched  nerve-process  sometimes  is  confined 
to  the  gray  cortex  in  the  vicinity  of  the  cell, 
sometimes  extends  to  the  molecular  zone, 
where    richly    branched    it    terminates    (Fig. 

124,  5,  5')- 

The    last  two   zones   contain   numerous 

medullated  nerve-fibers.  The  same  are 
arranged  in  thick  "  radiating "  bundles,  which  resolve  into  single 
fibers  near  the  zone  of  the  small  pyramidal  cells  (Fig.  123).  These 
bundles  are  formed  by  (i)  the  descending  medullated  nerve-pro- 
cesses of  the  large  and  the  small  pyramidal  cells,  by  (2)  thick  medul- 
lated nerve-fibers  of  unknown  origin,  that  ascend  from  the  white  sub- 
stance toward  the  cortex  (Fig.  1 24,  6),  where  they  repeatedly  divide  and 
form  the  "  superradial  "  and  the  tangential  plexus  (Fig.  123),  and  finally 
end  in  free  branches.  Another  set  of  medullated  nerve-fibers  runs  trans- 
versely to  the  radiating  bundles  and  forms  the  "  interradial  "  reticulum  ; 
this  is  somewhat  condensed  toward  the  superradial  reticulum  and  thus 
represents  the  stripe  of  Gcnnari  or  Baillarger  (Fig.  123).      This  and  the 


Nerve-process. 

Fig.  125. — Pyramidal  Cell  from 
A  Perpendicular  Section  of 
THE  Cerebral  Cortex  of 
Adult  Man.  X  120.  The  ter- 
minal branches  of  the  dendrites 
running  toward  the  molecular 
layer  are  not  visible.  Technic 
No.  79  b. 


THE    NERVOUS    SYSTEM.  20I 

interradial  reticulum  are  composed  of  the  medullated  collaterals  of  the 
nerve-processes  of  the  pyramidal  cells. 

The  structure  of  the  cerebral  cortex  is  modified  in  certain  localities. 
In  the  hippocampal  and  the  uncinate  convolution  the  tangential  fibers 
are  present  in  larger  numbers  and  form  an  expanded  net-like  white  layer, 
the  substantia  rcticulans  alba.  In  the  vicinity  of  the  calcarine  fissure  the 
stripe  of  Gennari  is  developed  into  the  bundle  of  Vicq  d' Asyr,  which 
may  be  seen  by  the  unaided  eye.  Furthermore,  greater  *  or  lesser 
deviations  occur  in  many  localities,  which  render  a  classification  accord- 
ing to  the  foregoing  description  much  more  difficult. 

Finally  extensions  of  the  pia,  that  penetrate  in  company  with  the 
blood-vessels,  and  neuroglia  participate  in  the  construction  of  the  cerebral 
cortex. 


Blood-vessel. 


Short-rayed  cells.  Long-rayed  cell. 

Fig.  126.— From  Sections  of  the  Brain  of  Adult  Man.     X  280.    Technic  No.  79  b. 

Neuroglia. — This  like  that  of  the  spinal  cord  consists  of  ependymal 
cells  and  of  astrocytes.  In  the  embryo  the  peripheral  processes  of  the 
former  extend  to  the  free  surface.  Of  the  latter  two  varieties  are  dis- 
tinguished. The  elements  of  the  one  variety  are  characterized  by  their 
small  cell-body  and  long,  rigid,  little-branched  processes,  of  which  the 
most  delicate  rest  like  a  short  turf  on  the  cell-body  ;  they  are  called 
long-rayed  cells  (Fig.  1 26),  and  chiefly  occur  in  the  white  substance.  The 
elements  of  the  other  variety,  the  short-rayed  cells  (Fig.  1 26),  have  short, 
gnarled,  richly  branched  processes  and  are  mainly  found  in  the  gray 
substance,  where  they  are  in  intimate  relation  with  the  blood-vessels,  to 


*  Regarding  the  minute  structure  of  the  cortex   of  the  cornu  ammonis  and  the  bulbus 
olfactorius,  the  reader  is  referred  to  special  text-books. 


202  HISTOLOGY. 

the  walls  of  which  they  are  often  attached  by  one  thicker  process  (Fig. 
126).*  On  the  surface  of  the  cerebral  cortex  there  is  a  glia-zone  formed 
by  the  ends  of  the  thitherward  extending  processes  of  the  glia-cells. 

THE    CEREBRAL    GANGLIA. 

The  gray  substance  of  the  cerebral  or  basal  ganglia  consists  of 
ganglion  cells  differing  in  size,  medullated  nerve-fibers,  and  neuroglia. 
The  macroscopic  variations  in  color  depend  on  the  different  proportions 
in  which  the  multipolar  ganglion  cells  and  the  nerve-fibers  are  mingled  : 
wealth  of  ganglion  cells  is  rendered  perceptible  by  a  dark  red-brown 
color,  profusion  of  nerve-fibers  by  a  pale  yellow-gray  color. 


THE    GRAY    SUBSTANCE    OF    THE    VENTRICLES. 

The  gray  substance  of  the  ventricles  extends  from  the  floor  of 
the  fourth  ventricle  through  the  cerebral  aqueduct  (Sylvii)  into  the  third 
ventricle,  and  to  the  tuber  cinereum  and  the  infundibulum.  It  is  of  especial 
interest  as  the  centers  of  origin  of  the  cranial  nerves.  It  is  composed  of 
neuroglia,  nerve-fibers,  and  ganglion  cells  ;  the  majority  of  the  latter  are 
multipolar  and  in  certain  localities  are  distinguished  by  their  size  (^.  g. 
in  the  nucleus  of  the  hypoglossal  nerve),  or  by  their  peculiar  form  (the 
spherical  ganglion  cells  in  the  upper  pair  of  the  corpora  quadrigemina). 

The  ependyma,  an  extension  of  the  neuroglia  and  the  cylinder  cells 
lining  the  central  canal  of  the  spinal  cord,  lines  the  continuation  of  the 
canal  (the  floor  of  the  fourth  ventricle,  the  cerebral  aqueduct,  the  inner 
surface  of  the  third  and  of  the  lateral  ventricles).  The  cylindric  or  cubical 
cells  of  the  ependyma  of  the  ventricles  in  the  newborn  and  in  part  also  in 
the  adult  possess  cilia. 

The  Cerebellar  Cortex. 
The  cerebellar  cortex  consists  of  three  well-defined  strata  of  gray 
substance,  of  which  the  outer  and  inner  are  macroscopically,  the  mid- 
dle, on  the  contrary,  only  microscopically  perceptible  :  they  are  from 
within  outward,  the  gramdc  layer,  the  ganglio^nc  layer,  and  the  moleadar 
layer. 

*This  relation  is  regarded  as  evidence  that  the  neuroglia  has  not  only  a  mechanical  func- 
tion as  supporting  apparatus,  but  also  a  nutritive  function  as  conveying  apparatus  for  nutrient 
fluids.  The  glia-cells  are  said  also  to  be  the  means  by  which  the  myelin  furnished  by  the  blood 
is  transferred  from  the  vessels  to  the  nerve-processes  of  the  central  nervous  system  [cf.  remark  *, 
p.  112). 


THE    NERVOUS    SYSTEM. 


203 


I.  The  granule  stratum,  the  innermost,  is  characterized  by  its  rust 
color  and  consists  of  numerous  layers  of  small  cells,  that  by  the  ordi- 
nary methods  exhibit  a  proportionately  large  nucleus  and  a  very  slightly 
developed  protoplasm.  By  the  aid  of  Golgi's  method  it  becomes 
evident  that,  apart  from  the  glia-cells,  two  varieties  of  ganglion  cells 
are  present :  suiall  granule-cells  and  large  granule-cells.  The  former 
(Fig.  128)  are  multipolar  ganglion  cells*  with  short  dendrites  (D)  with 
claw-like  endings  and  a  delicate   nonmeduUated  nerve-process  (N),   that 


Grav  stratum. 


Ganglionic  stratum. 


Fig.  127. — From  a  Vertical  Section  of  the  Cerebellum  of  Adult  Man.    X  12.    Technic  No.  78. 


passes  vertically  into  the  outermost  layer  and  there  divides  into  two 
T-branches  that  run  lengthwise  to  the  convolutions,  parallel  to  the 
surface  of  the  same,  and  terminate  in  free  unbranched  ends.  The  small 
granule-cells  form  the  chief  mass  of  the  cellular  elements  of  the  gran- 
ule stratum.  Less  numerous  are  the  large  grannie-cells  (Fig.  129),  mul- 
tipolar ganglion  cells  more  than  twice  the  size  of  the  smaller  elements, 
the  ramifying  dendrites  of  which  extend  into  the  outermost  stratum, 
the  nerve-process   of  which,  running  in   the  opposite  direction,  rapidly 


*  Their  ganglion-cell  nature  has  recently  been  called  into  question,  because  fibrillse  are 
wanting  in  the  protoplasm  and  the  nucleus  does  not  possess  the  structure  typical  for  nerve-cells. 


204 


HISTOLOGY. 


divides  and  terminates  in  a  very  rich  ramification  penetrating  the  entire 
granule  stratum. 

A  dense  plexus  of  medullated  nerve-fibers  occurs  in  the  granule 
stratum  (Fig.  1 30,  3) ;  the  greater  part  of  these  fibers  come  from  the  white 
substance  of  the  cerebellum  and  at  the  boundary  between  the  granule 
and  the  ganglionic  stratum  form  a  layer  of  horizontal  bundles  (3')  running 
transverse  to  the  longitudinal  axis  of  the  convolutions,  from  which  fibers 


Gray 

stratum. 


N- 


Granule 
stratum. 


B 


I 


Nerve-plexus. 

Fig.  129. — Large  Granule-cell.    X  200. 


Fig.  128. — Small 
Granule-cell. 
X  400. 

From  sections  of  the  cerebellar  cortex  of  a  cat  six  weeks  old.    Technic  No.  So. 


ascend  into  the  gray  stratum  (3")-     ^  small  portion  of  this  plexus  is 
formed  by  the  medullated  nerve-processes  of  the  cells  of  Purkinje. 

2.  The  middle,  ganglionic  stratnin  of  the  cerebellar  cortex  consists 
of  a  simple  layer  of  very  large  multipolar  ganglion  cells,  the  cells  of  Pur- 
kinje (Fig.  64).  Their  somewhat  pear-shaped  body  sends  two  robust 
dendrites  into  the  gray  layer,  where  they  terminate  in  an  uncommonly 
rich  arborization  extending  to  the  free  surface  (Fig.  130,  4).     The  arbori- 


THE    NERVOUS    SYSTEM. 


205 


zation  does  not  extend  in  all  directions,  but  only  in  planes  transverse  to  the 
long  axis  of  the  convolution,  therefore  the  entire  ramification  can  be  seen 
only  in  transverse  sections  of  the  convolution.  From  the  opposite  pole 
of  the  cell  the  nerve-process  arises,  soon  acquires  a  medullary  sheath,  and 
passing  through  the  granule  stratum  enters  the  white  substance  of  the 
cerebellum  ;  while  still  within  the  granule  stratum  it  sends  off  collaterals 


Gray  stratum. 


Granule  stratum.    Medulla. 


Fig.  130.— Scheme  of  the  Cerebellar  Cortex,  sketched  from  specimens  prepared  according  to  technic 

No.  80. 

I,  Small  granule-cell ;  2,  large  granule-cell;  3,  plexus  of  nerve-fibers  ;  3',  horizontal  bundle;  3",  fibers  of 
the  gray  stratum  ;  4,  cell  of  Purkinje  ;  5,  basket-cell ;  6,  small  cortical  cell,  the  nerve-process  is  not 
represented,  a,  Glia-cell  of  the  gray  stratum;  b,  glia-cell  resembling  a  short-rayed  cell;  c,  long- 
rayed  cell. 


that  branch  there  and  in  part  run  back  between  the  cells  of  Purkinje  (Fig. 

130). 

3.  The  outer,  gray  stratinn  is  characterized  by  its  gray  color  and 
contains  two  varieties  of  ganglion  cells  : 

(a)  The  basket-cells  (large  cortical  cells),  multipolar  ganglion  cells, 
the  dendrites  of  which  chiefly  extend  toward  the  free  surface.  Their 
long,  at  first  thin,  subsequently  thick  nerve-process  runs  horizontally  in 


2o6 


HISTOLOGY. 


the  transverse  direction  of  the  convolutions  and  sends  a  few  collaterals 
toward  the  free  surface,  into  the  depths,  at  successive  intervals,  delicate 
branches  that  with  their  terminal  ramifications  surround,  basket-wise,  the 
bodies  of  the  cells  of  Purkinje  (Fig.  131).  Frequently  the  basket  also 
includes  in  its  embrace  the  initial  portion  of  the  nerve-process  of  the  cells 
of  Purkinje. 

(/?)  The  small  cortical  cells,  which  differ  from  the  basket-cells  in  this 
that  their  nerve-process  enters  into  no  relation  with  the  bodies  of  the 
cells  of  Purkinje.  Two  types,  united  by  transitional  forms,  can  be  dis- 
tinguished. ^\v&  first  /j'/^  exhibits  multipolar  ganglion  cells  ;  their  cell- 
body  is  of  equal  size  or  only  slightly  smaller  than  that  of  the  basket-cells, 


Embryonal  su-  f 
perficial  gran-  [ 
ule  stratum.        / 


Gray  stratum. 


Part  of  the 
granule    i 
stratum. 


Dendrites.  Nerve-process. 


Cells  of  Purkinje. 


Fig.  131. — Basket-cell  from  a  Section  through  the  Cerebellar  Cortex  of  a  Six-week-old  Cat. 
X  240.  The  five  cells  of  Purkinje  were  not  blackened  but  were  plainly  visible;  only  the  outlines  of 
their  bodies  are  sketched.    Technic  No.  80. 


their  few  (from  2  to  5)  dendrites,  like  those  of  the  Purkinje  cells,  he  in 
the  transverse  planes  of  the  convolutions,  their  thin  nerve -process  is  very 
long  (i  mm.  and  over),  occasionally  exhibits  loop  formations,  ^nd  is 
characterized  by  a  very  rich  initial  ramification  (Fig.  132),  the  terminal 
ramification  being  scanty.  The  cortical  cells  of  the  second  type  are  in 
general  somewhat  smaller  and  their  short  nerve-process  ramifies  in  the 
immediate  vicinity. 

The  elements  of  the  first  type  form  the  chief  mass  of  the  relatively 
numerous  small  cortical  cells  and  occur  in  the  entire  thickness  of  the 
gray  stratum,  more  profusely  in  the  superficial  than  in  the  deep  parts. 
The  cells  of  the  second  type  are   found  everywhere  in  the  gray  stratum. 


THE    NERVOUS    SYSTEM. 


207 


The  medullated  nerve-fibers  occurring  in  the  gray  stratum  are  pro- 
cesses of  the  plexus  of  the  granule  stratum  and  partly  pass  toward  the 
free  surface,  where  after  loss  of  the  medullary  sheath  they  terminate  in 
free  ramifications  between  the  protoplasmic  arborizations  of  the  Purkinje 
cells,  partly  they  run  horizontally  between  the  bodies  of  the  cells  of  Pur- 
kinje, longitudinally  to  the  convolutions  (Fig.  130,  3'). 

The  neuroglia  of  the  cerebellum  consists  of  (i)  cells,  the  small  body 
of  which  lies  at  the  outer  boundary  of  the  granule  layer  and  sends  a  few 
short  processes  into  the  depths,  but  many  long  processes  in  a  straight 
course  toward  the  free  surface,  where  they  terminate  in  a  triangular  ex- 
pansion (Fig.  130,  a)  and  in  this  way  form  a  relatively  thick  peripheral 
glia-layer ;    (2)    also    of   stellate  elements    resembling    the    short-rayed 


Initial  rami-     Nerve- 
fication.        process. 


Fig.  132. — A  Small  Cortical  Cell  of  the 
First  Type.  From  a  Section  of  the 
Cerebellar  Cortex  of  Adult  Man. 
X  173.     Technic  No.  So. 


Fig.  133. — Two  Glia-cells  from  a 
Section  through  the  Cerebel- 
lar Cortex  of  Adult  Man.  X  90. 
On  the  right  the  body,  P,  and  the 
dendrites,  P ,  of  a  cell  of  Purkinje 
are  sketched  in  outline  to  demon- 
strate the  difference  between  this 
element  and  the  glia-cells.  Technic 
•No.  80. 


cells  of  the  cerebral  cortex  (Fig.  130,  b) ;  they  occur  in  all  the  strata 
(Fig.  133).      In  the  white  substance  typical  long-rayed  cells  are  found. 

So  long  as  the  cerebellar  cortex  is  not  fully  developed  a  series  of 
peculiarities  exists  that  is  wanting  in  the  adult.  In  embryos  and  young 
animals  there  is  over  the  as  yet  slightly  developed  gray  stratum  a  super- 
ficial granule  stratum  (Fig.  131)  ;  the  structures  in  the  granule  stratum 
described  under  the  name  of  "moss-fibers"  are  developmental  forms 
of  medullated  nerve-fibers  ;  of  like  significance  are  the  "  climbing  plex- 
uses," which  are  found  in  the  neighborhood  of  the  ramifying  protoplas- 
mic processes  of  the  cells  of  Purkinje. 

The  union  of  the  elements  of  the  cerebellum  is  only  by  contact, 
not  by  direct  connection. 

The  zvJiite  substance,  the    "  medulla,"  of  the   cerebrum    and  of  the 


208 


HISTOLOGY. 


cerebellum,  apart  from  the  elements  of  the  supporting  framework 
(connective  tissue  and  neuroglia),  consists  throughout  of  medullated 
nerve-fibers,  without  a  neurilemma  and  varying  in  thickness  from  2.5 
to  7  fx. 

The  hypophysis  cerebri  (pituitary  body)  is  composed  of  two  geneti- 
cally different  parts  :  (i)  2.  posterior  small  lobe  that  belongs  to  the  brain 
and  is  a  continuation  of  the  infundibulum  ;  it  contains  delicate,  much- 
branched  nerve-fibers,  that  form  a  very  fine  plexus,  and  connective  tissue, 
many  blood-vessels,  and  cells  that  closely  resemble  bipolar  or  multipo- 
lar ganglion  cells,  but  the  nature  of  which  is  still  uncertain ;  (2)  an 
antei'ior  larger  lobe  derived  from  a  diverticulum  of  the  embryonal  oral 
cavity;  this  lobe  contains  gland  follicles  embedded   in    loose,    vascular 


Solid  gland  folli- 
cle. 


Portion  of  an- 
terior lobe. 


Portion  of  pos- 
terior lobe. 


Hollow  gland 
follicle. 


Blood-vessel  con- 
taining blood 
corpuscles. 

"  Colloid"  sub- 
stance. 


Multipolar  cell. 


Connective-tissue 
fibers. 


Fig.  134. — Portion  of  a  Horizontal.Section  of  a  Human  Pituitary  Body,  showing  the  boundary 
line  between  the  anterior  and  the  posterior  lobe.  Two  gland  follicles  on  the  left  contain  each  a  dark 
epithelial  cell.     >(  220.     Technic  No.  Si. 


connective  tissue,  the  majority  of  which  are  solid  and  filled  with  some- 
times clear,  sometimes  granular,  cubical  epithelial  cells,  occasionally 
containing  vacuoles  (Fig.  134).  Only  a  few  of  the  follicles,  toward  the 
border  of  the  smaller  lobe,  are  hollow  and  occasionally  contain  a  mass 
resembling  the  colloid  substance  of  the  thyroid,  that  did  not  originate  in 
the  granules  which  are  to  be  seen  in  many  of  the  epithelial  cells. 

The  pineal  body  (corpus  pineale,  epiphysis)  is  derived  from  a  fold  of 
the  wall  of  the  primitive  brain  vesicle  and  consists  of  (epithelial)  cells, 
some  of  which  have  delicate  processes,  and  of  a  connective-tissue  envel- 
ope from  which  processes  extend  into  the  interior  of  the  organ.*    Almost 


■*In  the  pineal  body  of  the  ox  cross-striated  muscle-fibers  have  been  found. 


THE    NERVOUS    SYSTEM. 


209 


invan'abl}'  "brain  sand"  [accrvnltis  cerebri)  \9,  found  in  the  pineal  body, 
rounded  concretions  from  5  //  to  i  mm.  in  size,  with  an  uneven,  mul- 
berry-like surface  (Fig.  135).  They  are  composed  of  an  organic  basis, 
calcium  carbonate  and  magnesium  phosphate. 

Not  infrequently  (especially  in  advanced  life)  there  occur  in  the 
brain  substance  round  or  discoid  bodies  exhibiting  distinct  stratification, 
which  stain  violet  on  treatment  with  iodin  and  sulfuric  acid,  therefore  are 
related  to  amylum  (Fig.  1 36  ci).  These  corpuscula  aniylacca,  almost  con- 
stant on  the  walls  of  the  ventricles  of  the  brain,  are  also  present  in  many 
other  localities,  as  well  in  the  gray  as  in  the  white  substance,  and  in  the 
optic  nerve.  Closer  investigation  reveals  the  presence  of  a  homogeneous 
capsule  provided  with  a  few  processes.  They  are  glia-cells  trans- 
formed by  amyloid  infiltration. 


Fig.  135.— Brain  Sand  from  the  Pineal  Body 
OF  A  Woman  Seventy  Years  Old.  X  50. 
Technic  No.  82. 


Fig.  136.— From  a  Teased  Preparation  of  Gray 
Substance  from  the  Wall  of  a  Ventricle 
of  the  Human  Brain.  X  240.  a.  Corpuscula 
amylacea  ;  b,  myelin  drops  ;  c,  red  blood  corpus- 
cles; rf,  ependymal  cells;  e,  medullated  nerve- 
fibers;/',  ganglion  cell.     Technic  No.  83. 


The   Membranes  of  the  Central  Nervous  System. 

Two  connective-tissue  membranes  envelop  the  brain  and  the  spinal 
cord  :  the  dura  and  the  pia. 

The  dura  of  the  spinal  cord  {dura  mater  spinalis)  consists  of  compact 
fibrous  connective  tissue  and  numerous  elastic  fibers,  flat  connective-tissue 
cells  and  plasma  cells  (p.  93  and  Fig.  141).  The  inner  surface  is  cov- 
ered by  a  simple  layer  of  flat  epithelial  cells.  It  is  poor  in  nerves  and 
blood-vessels. 

The  dura  of  the  brain  {dura  mater  cerebralis)  is  at  the  same  time 
the  periosteum  of  the  inner  surface  of  the  cranium  and  consists  of  two 
lamellse  :  (i)  an  inner,  which  corresponds  to  the  dura  of  the  cord  and  is 
of  like  structure,  with  the  exception  that  it  is  richer  in  elastic  fibers,  and 
(2)  an  oitter  lamella  which  corresponds  to  the  periosteum  of  the  vertebral 
canal.      The   latter   is   composed   of   the   same   elements  as   the   inner 


210 


HISTOLOGY. 


lamella,  except  that  the  outer  fibers  run  in  a  different  direction ;  ante- 
riorly and  laterally  they  run  posteriorly  and  medianward,  while  the  inner 
iibers  run  from  the  anterior  median  region  posteriorly  and  lateralward. 
The  outer  lamella  is  rich  in  blood-vessels,  which  pass  from  it  into  the 
cranial  bones.  The  dura  is  rich  in  nerves,  of  w4iich  two  varieties  may 
be  distinguished,  vascular  nerves  and  free-ending  nervi  proprii. 

The  pia  of  the  brain  and  the  spinal  cord  is  a  two-layered  sack.  The 
outer  layer  (the  arachnoid  of  authors)  is  covered  on  its  free  surface  by  a 
simple  layer  of  epithelium  and  is  not  closely  attached  to  the  dura.  The 
inner  layer  (the  "  pia  ")  closely  envelops  the  surface  of  the  brain  and  the 
spinal  cord  and  sends  vascular  processes  into  their  substance.  The 
arachnoid  and  the  pia  are  joined  together  by  numerous  bands  and 
trabeculae  extending  from  the  inner  surface  of  the  former  to  the  outer 
surface  of  the  latter.      Hernia-like  evagrinations  occur  on   the  outer  sur- 


Blood-vessels. 


Epithelium. 


Fig.  137.— Portion  of  the  Plexus  Chorioideus  of  Adult  Man.  X  So.  x.  Blood-vessel  in  optical 
cross-section.  The  large  dots  in  the  epithelium  are  not  nuclei,  but  pigment  and  fat-granules. 
Technic  No.  84  b. 


face  of  the  arachnoid  in  certain  localities,  in  particular  near  the  superior 
longitudinal  sinus,  which  push  the  attenuated  dura  before  them  and  pro- 
ject into  the  venous  sinus.  These  are  the  so-called  arachnoidal  granu- 
lations [Pacchioni),  which  were  long  regarded  as  pathologic.  The  pia  is 
composed  of  delicate  connective-tissue  bundles  and  plate-like  cells,  which 
cover  the  inner  surface  of  the  arachnoid,  the  bands  and  the  trabecule. 

It  is  the  carrier  of  numerous  blood-vessels,  that  likewise  possess  nerves. 
But  whether  the  vessels  occurring  in  the  brain  and  in  the  spinal  cord  are  en- 
circled by  networks  of  nerves  is  still  questionable. 

The  telcB  chorioidecB  and  the  plexus  chorioidei  consist  of  connective 
tissue  and  numerous  blood-vessels,  the  fine  ramifications  of  which  are 
united  in  lobules  that  are  suspended  within  the  ventricles.  They  are 
covered  by  a  simple  layer  of  cubical  epithelial  cells,  ciliated  in  the  new- 
born, which  enclose  pigment  granules  and  also  oil  globules. 


the  nervous  system.  211 

The  Vessels  of  the  Central  Nervous  System. 
The  blood-vessels  of  the  central  nervous  system  form  a  narrow- 
meshed  capillary  network  in  the  gray,  a  wide-meshed  network  in  the 
white  substance,  which  are  everywhere  connected  with  each  other.  The 
capillaries  of  the  cerebral  cortex  open  into  veins  that  do  not  take  their 
origin  in  the  cortex,  but  beneath  in  the  white  substance  and  from  there 
traverse  the  cortex  and  go  to  the  veins  lying  in  the  pia.  Therefore  the 
blood  in  the  capillaries  must  traverse  the  entire  cortex  before  it  empties 
into  the  veins.  All  the  blood-vessels  possess  a  second  so-called  adven- 
titial sheath,  which  often  consists  of  only  a  simple  stratum  of  epithelial 
cells  (see  further  below).  The  walls  of  the  intradural  venous  sinuses  are 
formed  by  a  membrane  of  flat  epithelial  cells. 

THE    lymph    paths. 

1.  Between  the  dura  and  the  arachnoid  there  is  a  capillary  fissure, 
the  subdural  space,  which  communicates  with  the  deep  cervical  lymph- 
vessels  and  lymph-nodes  (at  least  in  the  rabbit  and  the  dog),  with  the 
lymph  channels  of  the  peripheral  nerves,  with  the  lymph-vessels  of  the 
nasal  mucous  membrane,  with  the  small  clefts  (juice-canals)  in  the  dura, 
and  finally,  round  the  arachnoidal  granulations,  with  the  intradural 
venous  sinuses.      The  fluid  in  the  subdural  space  is  very  scanty. 

2.  The  subaraclinoid  space,  that  between  the  two  layers  ot  the  pia 
(or  arachnoid  and  pia),  communicates  with  the  lymph  channels  of  the 
peripheral  nerves,  with  the  lymph-vessels  of  the  nasal  mucous  mem- 
brane, with  the  interior  of  the  ventricles  of  the  brain  and  of  the  central 
canal  of  the  spinal  cord.  The  fluid  in  the  subarachnoid  space  is  very 
abundant ;  it  is  called  the  ccrebro-spinal  JIuid  (liquor  cerebro-spinalis). 

3.  The  spaces  occurring  within  the  adventitial  sheath  of  the  blood- 
vessels can  be  injected  from  the  subarachnoid  space.  They  are  called 
adventitial  lymph  spaces. 

The  spaces  filled  only  by  injecting  the  brain  substance  itself  cannot 
be  included  in  the  lymph  vascular  system.  These  spaces  occur  as  (i) 
pericelhdar  spaces,  surrounding  the  larger  ganglion  cells  of  the  cerebral 
cortex,  also  many  glia-cells  ;  as  (2)  perivascular  spaces  of  the  blood- 
vessels, that  formed  by  the  adventitial  sheath  excepted  ;  and  between  the 
pia  and  the  cerebrum,  as  (3)  the  epicerebral  space.  These  may  be  regarded 
as  an  independent  juice-canal  system. 


212 


HISTOLOGY. 


2.    THE  PERIPHERAL  NERVOUS  SYSTEM. 

The  Nerves. 
The  cerebrospinal  nerves  chiefly  consist  of  medullated  nerve-fibers 
differing  in  thickness  and  of  only  a  few  nonmedullated  nerve-fibers  ; 
therefore  by  direct  light  they  appear  white.  Their  mode  of  union 
agrees  in  many  respects  with  that  of  the  striated  muscle-fibers.  A  cor- 
responding sheath  formed  of  loose  connective  tissue  and  numerous  elas- 
tic fibers,  often  containing  clusters  of  fat-cells,  surrounds  the  entire 
nerve.  It  is  called  the  epinenrhun  (Fig.  138).  Processes  of  the  epi- 
neurium  in  the  interior  of  the  nerve  envelop  the  (so-called  secondary) 
nerve-fiber  bundles,  of  which  each  is  encircled  by  concentrically  curved 
lamellae  of  connective  tissue,  the  perinenriuni.  From  the  latter  connec- 
tive-tissue septa  extend  into  the  interior  of  the  (secondary)  nerve-fiber 


Fat-cells. 


7^^-- 


Artery  in  transverse  \ / 7     ^  ^  _^ 


Cross-section  of  bun- 
dles of  nerve-fibers. 


Epineurium. 


Perineurium. 


Endoneurium. 


Fig.  138. — Portion  of  a  Cross-section  of  the  Human  Median  Nerve.    X  20.    Technic  No.  85. 

bundles  ;  they  have  been  named  the  endoncnruLm  (endoneural-lamella  of 
the  nerve-bundle).  Finally,  delicate  lamellae  from  the  endoneurium,  the 
fiber  sheaths  (endoneural  sheath  of  the  nerve-fiber)  corresponding  to  the 
perimysium  of  the  single  muscle-fiber,  surround  each  individual  nerve- 
fiber.  These  sheaths  are  in  direct  connection  with  processes  of  the  dura 
and  the  pia.  The  perineurium  and  the  endoneural-lamellae  *  consist  not 
only  of  connective-tissue  fibers,  but  also  of  elastic  fibers  and  of  a  variable 
number  of  concentric  membranes  ;  each  membrane  is  formed  by  a  simple 
layer  of  flattened  connective-tissue  cells,  the    outlines  of  which   can   be 


*  The  tv^o  together  form  the  "  Henle's  sheath  "   of  authors. 


THE    NERVOUS    SYSTEM. 


213 


demonstrated  by  silver  staining.  The  fiber-sheaths,  in  addition  to  deli- 
cate connective-tissue  bundles,  also  consist  of  plate-like  cells.  Divi- 
sions (namely  collaterals)  of  the  peripheral  nerve-fibers  do  not  occur 
during  their  course,  but  at  the  periphery  ;  on  the  other  hand,  not  infre- 
quently a  variable,  large  number  of  nerve-fibers  branch  from  one  bun- 
dle of  nerve-fibers  to  join  another  bundle.  The  result  of  this  is  an  acute- 
angled  plexus  of  fiber-bundles. 

The  sympathetic  nerves  are  partly  more  white  and  partly  more  gray 
in  color,  depending  upon  the  greater  or  lesser  number  of  fine  meduUated 
nerve-fibers  present ;  for  example,  the  splanchnic  nerves  contain  many 
meduUated  nerve-fibers,  while  the  gray  sympathetic  nerves,  for  example 
the  branches  of  the  abdominal  and  pelvic  plexuses,  contain  only  a  very 
few  of  the  thinnest  meduUated  and,  on  the  other  hand,  numerous 
nonmedullated    nerve-fibers.      One    portion    of  the   meduUated    nerve- 


Blood-vesse.  ^ 

containing  v 

blood-cells.  '\uC 

Axis-cylinder. 

Medullary 
sheath. 


fflR*<  Perineu- 
rium. 

Y      Endoneu- 
rium. 


Fiber  sheath. 


Fig.  139. — Portion  of  a  Cross-section  of  the  Human  Median  Nerve.    X  220.    Technic  No.  85. 


fibers  are  continuations  of  the  spinal  nerves,  another  portion  are  nerve- 
processes  of  sympathetic  nerve-cells  ;  long  dendrites  of  sympathetic 
nerve-cells  occasionally  occur  in  the  course  of  the  sympathetic  nerves 
{cf.  p.  219).  The  nerve-fibers  are  grouped  together  and  held  in  bundles 
by  connectiv^e  tissue. 

The  blood-vessels  run  lengthwise  within  the  epineurium  and  form 
capillary  networks  with  elongated  meshes  ;  they  are  supported  by  the 
perineurium  and  the  endoneurium. 

The  lymph  cJiannels  occur  in  the  capillary  clefts  between  the  lamellae 
of  the  perineurium  and  between  the  individual  nerve-fibers,  so  that  each 
nerve-fiber  is  bathed  in  lymph.  They  are  in  communication  with  the 
subdural  and  the  subarachnoid  space,  but  not  with  the  lymph-vessels 
accompanying  the  nerve. 


2  14  histology. 

The  Ganglia. 

Ganglia  are  groups  of  nerve-cells  intercalated  in  the  course  of  the 
peripheral  nerves.  Usually  they  are  macroscopically  visible.  All  gan- 
glia consist  of  small  bundles  of  nerve-fibers,  between  which  lie  ganglion 
cells,  partly  arranged  in  rounded  groups,  partly  in  longitudinal  rows 
(Fig.  140).  A  connective-tissue  capsule,  an  extension  of  the  perineu- 
rium, envelops  the  outer  surface  of  the  ganglion  and  sends  into  the 
interior  processes  for  the  support  of  the  nerve-fibers  and  the  ganglion 
cells.  The  ganglia  are  very  rich  in  blood-vessels,  the  capillaries  of 
which  surround  the  individual  cells.  Respecting  the  minute  structure, 
differences  exist  between  the  spinal  ganglia  and  the  sympathetic  ganglia. 

The  spinal  ganglia  possess  large,   spherical,  often  pigmented  nerve- 


,--#1- 


Nerve-fiber 
bundle. 


Fat. 


Nerve-fiber  bundle.  Connective  tissue. 

Fig.  140.— Longitudinal  Section  of  a  Spinal  Ganglion  of  a  Calf.    X  20.    (Schaper.) 

Technic  No.  86. 

cells,  the  vesicular  nucleus  of  which  encloses  a  large  nucleolus.  Each  cell 
is  enveloped  in  a  "  nucleated  capsule  "  (Fig.  141),  which  consists  of  flat, 
concentrically  stratified  connective-tissue  cells  and  is  prolonged  on  to 
the  process  of  the  ganglion  cell  as  the  fiber-sheath.  In  embryonal  life 
the  majority  of  the  nerve-cells  of  the  spinal  ganglia  are  bipolar,  the  pro- 
cesses springing  from  opposite  poles  of  the  cell.  In  the  course  of 
development  the  portion  of  the  cell-body  from  which  the  processes  arise 
becomes  attenuated,  stalkwise,  to  one  fiber,  one  process,  from  which 
the  primordial  two  processes  proceed  ;  thus  the  cell  becomes  unipolar.  * 

*  Isolated  bipolar   cells    also   occur  in   the  adult ;  they  may  be  regarded  as  elements 
arrested  in  their  development. 


THE    NERVOUS    SYSTEM,  21$ 

Recent  investigations  made  on  domesticated  mammals,  by  the 
methylene-blue  method  (p.  42),  teach  us  that  we  must  distinguish  differ- 
ent cell-types  : 

Type  I.  (a)  Large,  round  nerve-cells  ;  their  nerve-process,  spirally 
wound  in  its  initial  portion,  arises  from  a  conical  eminence  of  the  proto- 
plasm and  near  to  its  exit  from  the  cell  receives  a  medullary  sheath  and  a 
neurilemma  ;  after  sending  off  several  delicate  collaterals  it  divides  after 
a  shorter  or  longer  interval,  uniformly  at  the  niveau  of  a  node  of  Ranvier, 
T-  or  Y-shape  (p.  114)  in  two  (Fig.  142,  i)  or  three  (Fig,  142,  3) 
branches.*  One  of  these,  the  cellulipetal  branch,  passes  as  the  axis- 
Nucleus. 


Protoplasm. )iz_:  -    - — ''-Tr ~U Nucleolus. 


Nucleated  capsule. 


Nucleated  sheath  seen 
from  the  surface. 


a'^  > 


„       ,,        ^  X      -        .'   '      %    "*         "'--O   '  ' 'C?     'i^.' Plasma  cells. 

Bundles  of  cross-sec-     /  -'    •  <^    Q    fy.       .  '     £>^~' 


tioned  nerve-fibers. 


Perineurium.    ' ~^ \,i^ '  -y,^'  /''-■ ' 


^.^9 


Fig.  141.— From  a  Cross-section  of  the  Gasserian  Ganglion  of  Man.  X  240.  The  cell-processes 
cannot  be  seen.  At  X  the  protoplasm  of  the  ganglion  cell  has  retracted  and  simulates  a  process.  In 
the  axis  of  the  transversely  cut  nerve-fibers  the  axis-cylinders  are  seen  in  section.     Technic  No.  S6. 

cylinder  of  a  sensory  fiber  to  the  periphery  of  the  body  ;  the  other,  the 
cellulifugal,  usually  slighter  branch  runs  as  a  constituent  of  a  dorsal 
nerve-root  to  the  spinal  cord,  in  the  gray  substance  of  which  it  termi- 
nates in  a  free  ramification  (p.  193).  Thus  in  a  measure  each  spinal 
ganglion  cell,  by  its  yet  undivided  process,  is  intercalated  in  the  course 
of  its  sensory  nerve-fiber. 

{U)  Small,  round  nerve-cells  (Fig.  142,  4),  that  are  distinguished 
from  the  large  cells  only  by  their  delicate  nerve-process,  that  receives 
no  medullary  sheath  or  only  scattered  traces  of  such  a  cover. 


*Each  of  the  two  branches  may  divide  once  again;  of  the  twigs  proceeding  from  the 
peripheral  branch  the  one  runs  in  the  ventral,  the  other  in  the  dorsal  ramus  of  the  spinal 
nerve  (Fig.  142,  2). 


2l6 


HISTOLOGY. 


Type  II.  Spherical,  unipolar  cells,  the  process  of  which,  after  re- 
ceiving a  medullary  sheath  and  a  neurilemma,  repeatedly  divides  into  a 
large  number  of  meduUated  nerves  (Fig.  142,  6).  These  after  losing 
their  medullary  sheath  approach  the  cells  of  the  first  type  and  form  a 
pericapsular  plexus  lying  upon  the  nucleated   capsule   of  these  cells  ; 


Spinal  ganglion. 


Motor  cell  of 
anterior  horn 


Blood-vessel. 


Ventral  root. 


Dorsal 
ramus. 


Ventral  ramus. 

Visceral  ramus. 

Cell  of  a  sympathetic  ganglion. 


Fig.  142. — Scheme  of  the  Nervous  Elements  of  a  Spinal  Ganglion,  Projected  from  Prepara- 
tions Produced  after  Technic  No.  i86  b.  The  sensorj'  fibers  are  represented  by  continuous  lines, 
the  sympathetic  fibers  by  dotted  lines,  the  motor  fibers  by  a  linear  series  of  dashes.  The  medullary 
sheaths  of  the  motor  fibers  of  the  ventral  root  have  not  been  drawn. 


from  this  arise  delicate  branches  which  pierce  the  capsule  and  resolve 
into  a  pericellular  plexus.  Each  cell  of  the  first  type  is  enveloped  in 
the  plexuses  of  several  cells  of  the  second  type  (Fig.  142,  3).  The 
number  of  the  cells  of  the  second  type  is  relatively  insignificant. 


THE    NERVOUS    SYSTEM.  21/ 

Possibly  to  be  regarded  as  modifications  of  the  second  type  are 
multipolar  nerve-cells,  that  besides  short  dendrites  possess  a  centrally 
and  a  peripherally  running  nerve-process  (Fig.  142,  7).  These  processes 
appear  to  become  medullated  nerves,  that  however  do  not  pass  beyond 
the  territory  of  the  ganglion.  The  multipolar  cells  are  present  only  in 
very  limited  number. 

The  cells  of  the  second  type,  possibly  also  of  the  first  type,  are 
wrapped  in  varicose  pericapsular  and  pericellular  networks  of  fibers, 
which  are  the  nonmedullated  endings  of  medullated  nerve-fibers  coming 
from  a  few  sympathetic  nerve-cells  of  the  sympathetic  ganglia.  Branches 
of  these  fibers  also  go  to  the  blood-vessels  (Fig.  142).  Thus  through 
the  cells  of  the  second  type  a  small  number  of  entering  sympathetic 
fibers  are  brought  into  close  relation  with  a  large  number  of  cells  of  the 
first  type. 

The  fact  ascertained  by  careful  enumeration  that  in  a  spinal  ganglion 
there  are  many  more  ganglion  cells  than  there  are  cross-sections  of  medullated 
nerve-fibers  in  the  dorsal  nerve-root,  long  ago  permitted  the  conjecture  that 
further  complications  are  hidden  in  the  spinal  ganglion.  That  this  conjecture 
was  correct  is  testified  by  the  brilliant  discovery  of  ganglion  cells  of  the  second 
type,  the  nerve-process  of  which  does  not  pass  out  of  the  ganglion  ;  but  their 
small  number  is  not  sufficient  to  explain  the  discrepancy, — of  six  ganglion 
cells  to  one  medullated  nerve-fiber — even  if  to  them  we  add  the  few  multipolar 
ganglion  cells  regarding  the  course  of  the  nerves  of  which  little  is  yet  known. 
This  gap  is  filled  by  the  new  fact  that  the  nerve-processes  of  the  small  ganglion 
cells  of  the  first  type  are  chiefly  nonmedullated  (Fig.  142,  4).  Whether  there 
are  nerve-fibers  that  pass  through  the  spinal  ganglion  without  entering  into 
relation  with  its  cells  is  uncertain.  In  young  chick  embryos  such  fibers,  com- 
ing from  cells  of  the  anterior  horns,  have  been  demonstrated  ;  but  they  have 
not  been  found  in  any  mammal. 

Other  ganglia  possessing  the  same  structure  as  the  spinal  ganglia 
are  the  gasserian,  the  jugular,  the  plexus  nodosus  of  the  vagus,  the 
petrosal  and  the  geniculate.*  The  ganglia  of  the  auditory  nerve  (ganglia 
nervi  cochleae  et  nervi  vestibuli)  contain  bipolar  ganglion  cells. 

The  sympathetic  ganglia  consist  of  smaller,  often  pigmented,  uni- 
or  dinucleated  ganglion  cells  and  of  nerve-fibers. 

The  ganglion  cells  are  multipolar  f  and  fall  into  three  types  : 

*  The  latter  is  said  to  be  partly  a  sympathetic  ganglion. 

f  Among  the  cells  of  type  ii  are  some  that  have  all  processes  springing  from  one  or 
from  both  poles,  in  the  form  of  one  or  two  bunches  correspondingly  ;  such  cells  were  not  quite 
appropriately  named  uni-  or  bipolar  cells.  However,  the  sympathetic  ganglion  cells  of  fishes 
are  actually  bipolar ;  in  the  amphibia  ganglion  cells  occur  of  which  the  single  process,  subse- 
quently divided  T-shape,  is  embraced  by  a  "  spiral  fiber  "  that,  ending  in  a  free  ramification, 
weaves  itself  about  the  ganglion  cell  in  a  fashion  resembling  the  enveloping  plexus  of  the 
cells  of  the  spinal  ganglia. 


2l8 


HISTOLOGY. 


Type  I  (Fig.  143,  i).  Rounded  oval,  occasionally  flat  cells,  with 
numerous  short,  often  flattened  dendrites,  the  ramifications  of  which, 
beset  with  thorn-like  excrescences,  impart  to  the  cell  a  quite  character- 
istic appearance.  Their  nerve-process,  provided  with  very  delicate 
collaterals,  emerges  from  the  ganglion  as  a  nonmedullated  nerve-fiber 

Motor,        Sensory'spinal  nerve-fiber. 


Nerve-processes 


Nerve  trunklet. 


Smooth  muscle-fibers 


Sympathetic?  nerve- 
fiber. 


View  in  section  of  peri- 
capsular  plexus. 


Surface  view  of  peri- 
capsular  plexus. 


stellate  cell. 


Nerve-process. 


Lamellar  corpuscle 


Fig   143.— Scheme  of  the  Elements  of  Two  Sympathetic  Ganglia,  prepared  after  Technic  No. 
186  b.     1,  2,  3.  Cells  of  the  first,  second,  and  third  types. 

in  a  nerve  trunklet  and  finally  terminates  on  smooth  muscle-fibers  (cf. 
p.  "227).  The  large  majority  of  the  sympathetic  ganglion  cells  is  com- 
posed of  these  motor  elements.  , 

Type  II  (Fig.  143,  2).  Polygonal  cells,  the  dendrites  of  which  do 
not  like  those  of  types  i  and  iii  remain  confined  to  their  ganglion,  but 
always  as  very  slender  fibers  closely  resembling  nerve-processes  enclosed 


THE    NERVOUS    SYSTEM.  2ig 

in  nerve  trunklets  extend  into  neighbor  ganglia.*  Their  nerve-pro- 
cess enters  with  the  dendrites  into  a  nerve  trunklet,  either  as  a  nonmed- 
uUated  or  as  a  medullated  nerve-fiber,t  of  which  the  manner  of  termi- 
nation is  not  yet  definitely  established.  The  cells  of  type  ii  are  regarded 
as  sensory  elements. 

Type  III  (Fig.  143,  3).  The  cells  resemble  those  of  type  ii  ;  their 
long,  ramifying  dendrites  penetrate  between  the  neighboring  nerve-cells 
through  to  the  periphery  of  the  ganglion,  where  they  form  a  "  gen- 
eral X  peripheral  plexus."  Their  nerve-process  enters  into  a  nerve 
trunklet  as  a  nonmedullated  fiber  ;  the  termination  is  unknown.  The 
number  of  the  cells  of  type  iii  is  insignificant ;  they  are  entirely  wantmg 
in  the  smaller  ganglia. 

All  sympathetic  ganglion  cells  are  enveloped  in  a  capsule  (  "  nu- 
cleated sheath,"  Fig.  141),  that  continues  on  the  nerve-process  and  also 
on  the  coarser  dendrites. 

The  sympathetic  ganglia  contain,  besides  these  nervous  cells,  chromaffine 
cells  (p.  220 )  and  many  stellate  cells  provided  with  long  outrunners  (Fig. 
143),  that  mostly  are  applied  to  the  walls  of  the  blood- and  lymph-vessels; 
such  cells  occur  also  in  many  other  localities  of  the  body,  for  example  in  the 
intestinal  villi,  in  glands,  in  the  tongue,  and  very  probably  are  of  connective- 
tissue  nature. 

The  nerve-fibers  of  the  sympathetic  ganglia  are  : 

(a)  Spinal  nerve-fibers,  medullated,  that  simply  traverse  the  ganglion 
or,  after  loss  of  their  medullary  sheath,  with  a  relatively  coarse  terminal 
ramification  form  a  pericellular  plexus  around  the  cells  (probably  of 
type  i).  The  collaterals  of  such  nerves  behave  in  the  same  way  (Fig. 
143).  Also  sensory  nerve-fibers  coming  from  end-organs  (lamellar 
corpuscles,  p.  222)  pass  through  the  ganglion  (Fig.  143). 

(d)  Nonmedullated  nerve-fibers,  that  with  their  delicate,  varicose 
terminal  ramifications  form  a  pericapsular  plexus.  It  is  conjectured  that 
these  fibers  are  sympathetic  in  nature. 

The  ciliary,  spheno-palatine,  otic,  and  submaxillary  ganglia  belong  to 
the  sympathetic  ganglia. 

■^  See  also  the  Nerves  of  the  Stomach  and  of  the  Intestines,  (plexus  of  Meissner). 

f  The  medullary  sheath  does  not  appear  until  after  the  fiber  has  left  the  ganglion,  often 
in  very  great  remoteness  from  the  cell-body  ;  this  was  overlooked  by  some  investigators  ;  the 
theory  they  proclaimed,  that  all  nerve-fibers  originating  from  sympathetic  cells  are  nonmedul- 
lated, is  therefore  erroneous. 

i  The  expression  "general"  is  opposed  to  the  representation  of  Cajal,  according  to 
which  each  individual  nerve-cell  is  enclosed  in  a  dendrite  basket,  which  by  no  means  is 
invariably  the  case. 


220 


HISTOLOGY. 


In  conclusion  the  paraganglia  must  be  considered  here  ;  they  are  balls  or 
cords  of  cells  that  originate  in  the  embryonal  anlages  of  the  sympathetic 
ganglia,  and  are  distinguished  by  their  staining  yellow-brown  when  fixed  in  solu- 
tions of  chromic  acid  or  its  salts.  For  this  reason  the  cells  are  named  chromafflne 
cells.  The  paraganglia  occur  in  more  or  less  intimate  connection  with  the  sym- 
pathetic nerve.  The  recently  discovered,  macroscopically  demonstrable  sym- 
pathetic accessory  organs  at  the  origin  of  the  inferior  mesenteric  artery  belong 
to  the  same  category.  Single  chromaffine  cells  or  small  groups  of  them  occur  as 
diffuse  infiltrations  in  the  interior  of  sympathetic  ganglia  and  nerves.  Finally, 
the  entire  medullary  substance  of  the  adrenal  bodies  of  the  higher  vertebrates 
consists  of  chromaffin e  cells. 


Stratum  corneum. 
Stratum  lucidum. 


Stratum  germina- 
/  tivum. 


Epidermis. 


Fig.  144. — Vertical  Section  of  the  Skin  of  the  Great  Toe  of  a  Man  Twenty-five  Years  of  Age. 
X  200.  The  cell-nuclei  of  the  stratum  germinativum  are  distinct  only  in  the  deepest  layer.  /,  Cells 
of  Langerhans  ;  «,  intraepithelial  nerve-fibers.  P,  Pi,  two  papillae  of  the  corium  ;  P  contains  a  capil- 
lary loop,  c,  of  which  only  one  limb  is  visible  ;  P'^  contains  a  tactile  corpuscle,  t,  with  two  approach- 
ing medullated  nerve-fibers,  m.     Both  papilla  contain  nonmedullated  nerve-fibers.     Technic  No.  88. 


The    Peripheral    Nerve-endings. 


TERMINATIONS    OF    THE    SENSORY    NERVES. 

The -peripheral  terminal  branches  of  the  sensory  nerves  either  are 
distributed  naked,  z.^  free  endings,  or  they  are  enclosed  by  epithelial  or 
connective-tissue  cells,  with  which  they  form  special  endings,  the  termi- 
nal corpuscles.  * 

The  free-nerve  endings  occur  in  this  manner.  The  nerve-fibers 
lose  their  medullated  sheath,  divide  repeatedly,  and  form  a  plexus  of 
primitive  fibrils  that  terminate  in  pointed  or  club-shaped  ends.     These 

*  The  nerve-endings  of  the  neuro-epithelial  cells  are  described  in  the  chapters  on  the 
special-sense  organs. 


THE    NERVOUS    SYSTEM.  221 

endings  chiefly  occur  in  stratified  epithelium.  They  have  been  demon- 
strated with  certainty  in  the  cornea  (see  the  Visual  Organ),  in  the  oral 
mucous  membrane  (see  the  Gustatory  Organ),  and  in  the  deeper  strata 
of  the  epidermis.  In  the  latter  cells  provided  with  long,  branched  pro- 
cesses, the  cells  of  Langcrlians  (Fig.  144),  occur;  these  were  formerly 
regarded  as  migrated  wandering  cells  (p.  93)  from  the  corium  and  it  is 
possible  that  a  few  of  them  may  really  have  such  an  origin  ;  but  the 
majority  are  transformations  of  degenerating  ordinary  epithelial  cells, 
for  all  the  transitional  forms,  from  the  typical  epithelial  cells  to  the 
stellate  bodies  in  question,  may  be  found. 

Sensory  nerves  have  been  found  also  in  the  muscles.  They  divide 
dichotomously  into  many  nonmedullated  fibers,  provided  with  a  neuri- 
lemma, and  terminate  in  delicate,  slender,  free  fibrils  between  the  muscle- 
fibers  (Fig.  153). 

The  terminal  corpuscles  may  be  divided  into  two  main  varieties  : 
the  tactile  cells  and  the  end-bulbs.  In  the  tactile  cells  the  nerve-fiber  ter- 
minates in  relation  with  one  or  two  cells  ;  in  end-bulbs  it  terminates  in  the 
interior  of  a  finely  granular  body,  the  so-called  inner  bulb. 


Epidermis. 


Tactile  meniscus. 


Xerve-fiber. 

Connective-tissue  sheath 
of  the  same. 


Fig.  14=;.— From  a  Vertical  Section  of  the  Skin  of  the  Great  Toe  of  a  Man  Twenty-five  Years 
Old.  X  240.  The  outlines  of  the  cells  and  the  nuclei  of  the  epidermis  can  only  be  indistinctly  seen. 
X.  Tactile  cells  in  the  corium,  resting  upon  the  ramifications  of  a  delicate  nerve-fiber.     Technic  No.  88. 


I.    TACTILE    CELLS. 

The  tactile  cells  ma}-  be  either  simple  or  compound,  {ci)  The  sim- 
ple tactile  cells  are  oval,  nucleated  bodies  measuring  from  6  to  12  « 
(Fig.  145),  which  occur  in  the  deepest  strata  of  the  epidermis  and  in  the 
outer  root-sheath  of  the  hairs  or  in  the  adjacent  portions  of  the  corium. 
The  tactile  cells  rest  on  the  tactile  meniscus,  a  crescentic  expansion  of  a 
nonmedullated  nerve-fiber. 

{b)  The  compound  tactile  cells  (Grandry's  and  Merkel's  corpuscles) 
consist  of  two  or  more  discoid  cells,  of  which  each  is  larger  than  a  simple 
tactile  cell  (15  a  high  and  50  n  broad),  and  contains  a  vesicular  nucleus. 
A  medullated  nerve-fiber  approaches  the  compound  tactile  cell  (Fig.   146) 


222 


HISTOLOGY. 


and  the  forks  of  the  divided  axis-cyhnder  clasp  a  flat  disk,  the  tactile 
disk  its),  that  hes  between  two  mutually  flattened  discoid  cells  {tz).  The 
nerve-fiber  loses  its  medullated  sheath  at  the  point  of  entrance  and  the 
perineurium  becomes  fused  with  the  connective  tissue  of  the  capsule  (/^) 
enveloping  the  tactile  cells.  The  compound  forms  consisting  of  two 
tactile  cells  are  named  twin  tactile  cells  {B  2),  those  consisting  of  three 
or  four  tactile  cells,  "simple  tactile  corpuscles"  {A,  B  i).  The  com- 
pound tactile  cells  have  only  been  found  in  the  skin  of  the  beak  and  of 
the  tongue  of  birds,  especially  in  web-footed  birds  ;  they  are  almost 
exclusively  situated  in  the  uppermost  strata  of  the  corium. 


Fig.  146.— From  Vertical  Skctions  of  the  Cere  of  the  Beak  of  a  Goose.  X  240.  A.  Compound 
tactile  cell  (simple  tactile  corpuscle),  cut  parallel  to  the  course  of  the  entering  nerve-fiber:  «,  medul-' 
lated  nerve-fiber  only  partially  met  by  the  section ;  a,  axis-cylinder  :  its  forks  here,  in  profile,  are  in- 
visible; ts,  tactile  disk  cut  vertically;  A,  connective-tissue  sheath;  tz,  tactile  cells.  B.  Two  com- 
pound tactile  cells  cut  transversely  to  the  plane  of  the  entering  nerve-fiber,  i.  "  Simple  tactile  cor- 
puscle," consisting  of  four  tactile  cells;  2,  twin  tactile  cells;  ts,  tactile  disks;  a,  axis-cylinders  in 
transverse  section,  before  dividing;  w,  medullated  nerve-fibers  ;  c,  corium.     Technic  No.  89. 


2.    END-BULBS. 

The  end-bulbs  are  spherical  or  oval  bodies  in  the  interior  of  which 
nerve-fibers  enter  and  terminate,  sometimes  in  a  simple,  sometimes  in  a 
branched  ending.     There  are  various  forms  of  end-bulbs. 

ia)  The  so-called  cylindrical  end-biilbs,  the  simplest  form  (Fig. 
147),  chiefly  consist, of  a  modified  extension  of  the  entering  nerve-fiber 
and  comprise  three  parts, — the  axis-cylinder,  the  inner  bulb,  and  the 
capsule.  The  capside  is  composed  of  flattened  connective-tissue  cells, 
the  continuation  of  the  fiber-sheath  (Fig.  139).  The  inner  bulb  is  a  finely 
granular  mass  which  exhibits  concentric  stratification  and  has  a  few 
nuclei  at  the  periphery.  The  nerve-fiber  loses  its  medullary  sheath  on 
entering  the  end-bulb,  in  which  the  axis-cylinder  ascends  as  a  flat  band 
and  terminates  near  the  upper  pole  in  a  free  rounded  or  club-shaped 
ending.  The  cylindrical  end-bulbs  are  found  in  the  tunica  propria  of 
mucous  membranes  ;  for  example,  in  the  scleral  conjunctiva  of  mam- 
mals and  in  the  oral  mucous  membrane. 

{b)  The  lamellar  corpuscles  (Vater,  Pacini)  are  transparent,  elliptical 


THE    NERVOUS    SYSTEM. 


223 


structures,  from  2  to  4. 5  mm.  long  and  i  to  2  mm.  thick,  and  like  the 
cylindrical  end-bulbs  consist  of  a  capsule,  an  inner  bulb,  and  an  axis- 
cylinder.  The  capsule  consists  of  a  large  number  of  concentric  cap- 
sules, one  within  the  other,  of  which  each  is  separated  from  its  neigh- 
bors by  a  simple  layer  of  flat  connective-tissue  cells.  Each  contains 
fluid  and  connective-tissue  fibers  running  longitudinally  and  trans- 
versely.      Like  the  capsule  of  the  c\'lindrical  end-bulbs,  so  these  capsules 


,-    Blood-vessel. 

Axis-cylinder. 

-  Inner  bulb. 

-  Sheath. 


Medullated 
nerve-fiber. 


Fig.  147.— Cylindrical  End-bulb  from  the  Con- 
junctiva OF  A  Calf.    X  240.     Techtiic  No.  90. 


-  Axis-cylinder. 


Inner  bulb 


Fig.  14S.— Small  Lamellar  Corpuscle  from 
THE  Mesentery  of  a  Cat.  X  50.  The  cells 
lining  the  capsules  can  be  recognized  by  their 
shaded  nuclei.  The  medulla  of  the  nerve- 
fiber  may  be  traced  to  the  inner  bulb.  Technic 
No.  qi. 


originate  from  the  connective-tissue  sheath  ot  the  entering  nerve-fiber. 
The  capsules  are  the  smaller  the  nearer  the  inner  bulb  they  lie.  At  the 
pole  opposite  the  entrance  of  the  nerve  they  are  not  seldom  connected 
by  a  cord  running  in  the  direction  of  the  inner  bulb,  the  intcrlauicllar 
ligament.  The  inner  bulb  is  like  that  of  the  cylindrical  end-bulbs  ;  in 
its  axis  runs  a  thick  axis-cylinder,  which  terminates  in  a  simple  or 
forked  end,  enveloped  in  the  delicate  end  ramification  of  a  second  thin 
axis-cylinder.  The  latter  is  visible  only  after  methylene  blue  staining. 
A  small  artery  accompanies  the  nerve-fiber  into  the  interior  of  the  cor- 
puscle, which  breaks  up  into  a  capillary  network  lying  between  the 
peripheral  lamellae  of  the  capsule. 

The  lamellar  corpuscles  partly  occur  in  superficial  situations  (abun- 
dantly in  the  subcutaneous  connective  tissue  of  the  palm  of  the  hand  and 
the  sole  of  the  foot,  more  sparingly  in  other  localities  of  the  skin,  on  the 
nipples,  in  the  territory  of  the  pudendal  nerve) ;  partly  in  deeper  situa- 
tions (in  the  vicinity  of  the  joints,   on  the  nerves  of  the  periosteum  and 


224  HISTOLOGY. 

the  bones,  in  tendons  and  their  sheaths,  in  fascise,  in  the  mesentery,  in 
the  neighborhood  of  the  pancreas,  and  in  different  parts  of  the  male 
genital  organs  of  mammals).  They  transmit  simple  pressure  sensations. 
The  corpuscles  of  Herbst  and  Key-Retzius,  occurring  in  birds,  are 
also  lamellar  corpuscles  ;  they  only  differ  in  being  much  smaller  and  in 
possessing  a  double  row  of  longitudinally  disposed  nuclei  in  the  inner  bulb. 
(c)  The  genital  ner've  corpuscles  of  the  lower  mammals  and  of  man 
are  spherical  or  oval  forms  (from  0.06  mm.  to  0.4  mm.  long),  and  con- 
sist of  a  finely  granular,  nonnucleated  inner  bulb  enveloped  in  a  connec- 
tive-tissue capsule  containing  cells  rich  in  protoplasm.  The  approaching 
medullated  nerve-fibers  make  several  turns  around  the  corpuscle,  lose 
their  medulla  and  divide,  while  the  fiber-sheath  and  the  neurilemma  pass 
into  the  capsule;  the  naked  axis-cylinders  penetrate  the  inner  bulb  at 
different  points,  undergo  rapid  division  and  form  a  dense  plexus  of 
fibrils  with  varicose  enlargements.*  Each  plexus  is  connected  by  deli- 
cate nerve  filaments  with  plexuses  of  neighbor  corpuscles. 

The  genital  nerve  corpuscles  lie  in  the  depths  of  the  corium  at  various 
distances  from  the  papillary  stratum  ;  in   the  papillae  only  smaller  cor- 
puscles, resembling  the  "  spherical  end-bulbs,"  are  found.      The  largest 
number  of  genital  nerve  corpuscles,  from  one  to  four  to  the  square  milli- 
meter, occurs  in  the  glans  penis  and  in  the  clit- 
oris.    The  so-called  spherical  end-bulbs  (in   real- 
ity they  are  sometimes  round,  sometimes  oval) 
have  a  similar  structure  ;  they  are  found  in  the 
conjunctiva  and  in  the  adjoining  portions  of  the 
cornea  of  man,  and  possess  a  greatest  diameter 
of  0.02  to  0.1    mm.       The  artictdar  nerve  cor- 
puscles belong  to  the  same  category. 

{ci)  The    tactile    corpuscles    (Wagner's    and 
Meissner's   corpuscles)  are  elliptical    structures, 

Fig.  149.— Tactile  Corpuscle        from  4O    tO     I  GO //.    long    and    3O    tO    60  U.    broad, 
FROM    A    Perpendicular  •        1   1  1  •  /t^- 

Section  of  the  Great      which  are  characterized  by  cross-markmgs  (rig. 

Toe  of  a  Man  Twkntv-  "^  o     \      o 

"Y?  Years  Old.    X  560.      I4q).     They  posscss  a  connectivc-tissue  capsule 

«,  Medullated  nerve-fibers;  ^^/  J    i  ^ 

tiVluisuesife^iih.'  ^Tnt     (Fig-  149.  ^0  with  flattened  cells,  the  boundaries 
ciei  are  invisible.   Technic      ^f  which,  as  wcU  as    their  trausvcrsely  placed 

nuclei,  produce  the  cross-striations  just  men- 
tioned. One  or  two  medullated  nerve-fibers  approach  each  tactile 
corpuscle  (Fig.  149,  ;/),  make  transverse  tours  encircling  the  lower 
pole   of   the   corpuscle,    part   with    their   neurilemma   and    fiber-sheath, 

*  In  imperfect  staining  the  varicosities  simulate  club-shaped  endings. 


THE    NERVOUS    SYSTEM. 


225 


which  blend  with  the  tissue  of  the  capsule,  then  lose  their  medullary 
sheath,  and  as  naked  axis-cylinders  enter  into  a  granular  substance  cor- 
responding to  an  inner  bulb  ;  there  they  form  a  complicated  plexus  beset 
with   varicosities  (£■).     The    tactile   corpuscles  he  in  the  papillae  of  the 


Terminal  ramification.        Tendon-bundle. 


—  Medullated  nerve-fiber. 


Muscle-fibers. 


Fig.  150. — Tendon-spindle  of  an  Adult  Cat.    X  So.    Technic  like  No.  92  a. 

corium  and  are  most  numerous  (twenty-three  to  one  square  millimeter) 
on  the  palm  of  the  hand,  on  the  finger-tips,  and  on  the  sole  of  the  foot. 


Medullated  nerve- 
fiber. 


^^     Axis-cylinder. 


Nucleus  of  a 
tendon-cell. 


Fig.  151.— a  Portion  of  the  Preparation  of  Figure  150.    X  345. 

In  connection  with  the  end-bulbs  the  tendon-  and  the  muscle-spindle, 
as  well  as  the  terminal  cylinder  of  Ruffini,  remain  to  be  considered. 

The  tciidoji-spindlcs  are  usually  spindle-shaped  expansions  of  th.e 
tendon  bundles  and  are  enveloped  in  a  well-developed  connective-tissue 
sheath.  The  one  end  of  the  spindle  passes  into  tendon  bundles,  the 
other  continues  into  muscle-fibers  (Fig.  i  50).      The  nerve-fibers  approach 


226 


HISTOLOGY. 


Medullated 
nerves. 


themiddle  of  the  spindle,  divide  repeatedly,  lose  their  medulla,  and  break 

up  into  a  richly  developed  ramification 
with  often  expanded,  clavate  ends 
(Fig.  151).  The  tendon-spindles  oc- 
cur in  all  tendons  in  man,  but  in  vary- 
ing number  ;  they  transmit  the  sensa- 
tion of  extension  and  enter  into  activity 
in  coordinated  movements. 

The  muscle -spindles  (muscle- 
buds)  are  clusters  of  delicate  muscle- 
fibers  that  are  enveloped  in  a  thick 
perimysium  sheath  (Fig.  iii)  and 
provided  with  many  nuclei  ;  the  ter- 
minal ramifications  of  the  approaching 
nerves  are  arranged  either  in  the  form 
of  spirals  and  rings  (Fig.  152,  above) 
or  of  blossom-like  sprays  with  clubbed 
ends  (Fig.  152,  below).  The  muscle- 
spindles  are  wanting  in  the  muscles  of 
the  eye,  pharynx,  esophagus,  larynx, 
in  the  ischio-  and  bulbo-cavernosus 
muscles,  in  the  diaphragm,  in  the  mi- 
metic facial  muscles.  They  react  to 
the  pressure  exercised  by  the  contrac- 
tion of  neighboring  muscles. 

The  terminal  cylinders  in  their 
end  ramifications  resemble  the  tendon- 
spindles  (see  the  chapter  on  the  skin). 


V\ 


TERMINATIONS  OF  THE  MOTOR  NERVES. 

The  small  nerve-trunks  supplying 
striated  muscles  divide  into  branches, 
these  subdivide  into  twigs  (nerve-fiber 
bundles)  that  anastomose  with  one 
another  and  form  a  plexus,  the  inter- 
muscidar  nerve-plexus.  In  the  terri- 
tory of  this  plexus  the  medullated 
nerve-fibers  undergo  numerous  divi- 
sions, so  that  the  sum  of  fibers  is  con- 
siderably increased.  The  twigs  of  the  plexus  divide  into  delicate  branches, 
consisting  oi  single  nerve-fibers,  each  one  of  which  finally  connects  with  a 


P'lG.  152. — Muscle-spindle  of  an  Adult  Cat 
X  135.    Techiiic  like  No.  92  a. 


THE    NERVOUS    SYSTEM. 


227 


muscle-fiber.    At  the  point  where  the  nerve-fiber  comes  into  contact  with 
the  muscle-fiber  it  tapers,  loses  its  medullary  sheath,  the  axis-cylinder 


Sensory  nerve- 
fibers. 


Muscle-fibers. 


Motor  plate. 


Medullated 
nerve-fibers. 


Nerve-fiber  / 
bundle. 


i»f,fl«TI»K*1J'(V1;1ir'^111H;: 


'^^-ii«Siiii|| 


Fig.  153. — Motor  Nerve-endings  of  Intercostal  Muscle-fibers  of  a  Rabbit.    X  150. 

Technic  No.  92  a. 


breaks  up  into  slightly  tortuous  terminal  branches  with  bulbous  ends 
(Fig.  153),  which  form  the  so-called  motor  {end^  plate  and  rest  upon  a 
rounded,  finely  granular  disk  containing  numerous  vesicular  nuclei.  Each 
muscle-fiber  possesses  at  least  one  motor 
plate  ;  it  lies  upon  the  sarcolemma. 

The  nerves  supplying  the  smooth  muscles 
form  a  plexus  from  which  bundles  of  nonmed- 
uUated  nerve-fibers  arise ;  the  latter  divide 
repeatedly  and  form  several  networks,  from 
which  finally  the  most  delicate  nerve-fibers 
arise.  These  apply  themselves  to  the  smooth 
muscle-fibers  and  often  are  slightly  thickened 
at  the  point  of  contact ;  probably  each  muscle- 
fiber  possesses  a  nerv^e-ending. 


Fig.  154. — Motor  Nerve-ending 
ON  A  Fiber  of  an  Ocular 
Muscle  of  a  Rabbit.  X  240. 
N.  Medullated  nerve-fiber;  A', 
nuclei  of  the  disk.  The  trans- 
verse stria;  are  distinct  only  in 
the  lower  half  of  the  nuiscle- 
fiber.     Technic  No.  92  b. 


The  Suprarenal  Body. 

The  description  of  the  suprarenal  (adrenal)  body  with  the  organs  of 
the  nervous  system  is  warranted  by  the  profusion  of  its  nervous  ele- 
ments, by  its  relations  to  the  central  nervous  system,  as  established  by 
experiment,  as  well  as  by  the  facts  of  comparative  anatomy. 

Each  suprarenal  body  consists  of  a  cellular  parenchyma  and  a  con- 
nective-tissue capsule,  which  sends  delicate  processes  into  the  interior  of 


228 


HISTOLOGY, 


the  organ,  and  contains  elastic  fibers  only  in  the  neighborhood  of  the 
blood-vessels  in  the  capsule  and  in  the  medulla,  but  not  in  the  cortex.  The 
parenchyma  consists  of  an  outer  stratum,  the  cortex,  which  surrounds  an 
inner  mass,  the  viediilla,  on  all  sides  (Fig.  155).*  The  cortex  is  of 
fibrous  texture,  of  a  yellow  color  when  fresh,  and  is  composed  of  cells 
about  15  fj.  in  size,  rounded  in  shape,  that  possess  a  coarsely  granular 
protoplasm,  sometimes  containing  fat  particles,  and  a  clear  nucleus.  In 
the  outer  zone  of  the  cortex  the  cells  are  grouped  in  oval  masses,  in  the 
middle  zone  they  are  arranged  in  cylindric  columns,  while  in  the  inner- 


Capsule. 


^^ 


Cortex.    Medulla.  Vein. 

Fig.  155. — Section  of  the 
Suprarenal  Body  of 
A  Child.  X  i5-  Tech- 
iiic  No.  93. 


Cortex. 


Zona  glomerulosa 


Zona  fasciculata 


Zona  reticularis. 


Cell-cords  of  the 
medulla. 


Nerve  in  transverse 
section. 


Ganglion  cells   — 

Bundles  ot  smooth  mus-  • — 
cle-fibers  in  transverse 
section. 


Veins  in  cross-section  =^ 


Fig.  156. — Section  of  a  Human  Suprarenal   Body.    X  50.    Technic 
No.  95. 


Medulla. 


most  zone  the  cells  lie  irregularly  scattered  in  a  reticulum  of  connective 
tissue  ;  the  cells  of  the  innermost  zone  are  characterized  by  their  pig- 
mentation. According  to  the  described  arrangement  the  cortex  is 
divided  into  :  i,  the  zona  glomerulosa  ;  2,  the  zona  fasciculata  ;  3,  the 
zona  reticularis  (Fig.  157).  The  medulla  in  the  fresh  state  is  sometimes 
lighter,  sometimes  darker  than  the  cortex  and  consists  of  chromaffine 
cells  (p.  220),  that  are  arranged  in  spherical  or  elliptical  cords  joined  in 
an  irregular  network. 


*  The  formations  on  the  ductus  deferens  and  in  the  broad  ligament  described  as  ruptured 
adrenals  consist  only  of  cortical  substance. 


THE    NERVOUS    SYSTEM.  229 

The  arteries  di\ide  in  the  connective-tissue  capsule  into  numerous 


Capsule. 


-    Zona  glomerulosa. 


\- —    Zona  fasciculata. 


7-. 


I.  '^j 


*.v 


Zona  reticularis. 


Medulla. 


Fig.  157.— Section  through  Corte.x  and  Medulla  of  the  Suprarenal  Body  of  Adult  Man. 

X  200.    (Schaper.) 

small  branches  that  penetrate  the  cortex  and   there  form  a  long-meshed 


230  HISTOLOGY. 

capillary  network,  which  passes  into  the  medullary  substance  where  the 
meshes  are  round.  From  the  latter  the  veins  proceed,  of  which  the 
larger  are  accompanied  by  longitudinal  strands  of  smooth  muscle-fibers. 
While  still  within  the  medulla  the  veins  unite  and  form  the  chief  vein, 
the  suprarenal  vein. 

The  numerous,  chiefly  nonmedullated  nerves  (in  man  about  33  small 
trunks)  come  principally  from  the  celiac  plexus  and  pass  with  the  arteries 
through  capsule  and  cortex  to  the  interior  of  the  medulla.  During  their 
course  they  give  off  a  few  twigs  to  the  capsule,  that  form  a  plexus  there  ; 
from  this  delicate  branches  descend  into  the  cortex  between  the  cell- 
groups  of  the  zona  glomerulosa  and  the  zona  fasciculata,  which  terminate 
on  the  surface  of  the  cell-clusters,  without  penetrating  between  the  indi- 
vidual cells.  Richer  is  the  nerve-plexus  of  the  zona  reticularis,  which 
originates  by  the  branching  of  fibers  that  descend  straight  through  the 
cortex  ;  it  also  surrounds  only  cell-groups.  In  the  medullary  substance 
the  nerve-plexus  is  extraordinarily  dense  ;  each  individual  cell  is  sur- 
rounded by  nerve-fibers.  In  the  medulla,  seldom  in  the  cortex,  groups 
of  sympathetic  ganglion  cells  occur.  Some  of  the  nerves  terminate  in 
the  walls  of  the  blood-vessels. 

TECHNIC. 

No.  73. — The  spinal  cord. — For  the  study  of  the  distribution  of 
the  white  and  the  gray  substance  the  spinal  cord  of  a  child  should  be 
fixed  in  toto  in  about  one  liter  of  Miiller's  fluid,  that  should  be  frequently 
changed  ;  after  four  or  five  months  thick  cross-sections  of  the  cervical, 
thoracic,  and  lumbar  regions  may  be  cut,  and  without  further  treatment 
mounted  in  dilute  glycerol  (p.  23),  or  after  the  customary  preliminary 
treatment  they  may  be  mounted  in  xylol-balsam. 

No.  74. — Tlie  spinal  cord ;  staining  of  medullated  fibers  after  Pal. — 
The  success  of  the  preparation  depends  especially  on  the  state  of  preserva- 
tion of  the  organ.  The  fresher  the  tissue  when  it  is  put  into  the  fixing 
fluid,  the  better  will  be  the  result.  The  entire  spinal  cord  should  be 
placed  in  a  large  quantity  of  Miiller's  flhid,  that  must  be  changed  daily 
during  the  first  week  and  frequently  thereafter.  If  it  is  desired  to  investi- 
gate only  portions  of  the  spinal  cord,  then  place  pieces  of  the  fresh  cord, 
about  2  cm.  long,  from  the  lower  cervical,  the  middle  thoracic,  and  the 
lumbar  region,  in  from  200  to  500  c.c.  of  Miiller's  fluid  or,  better,  sus- 
pend them  in  it.  In  four  or  six  weeks,  during  which  time  the  fluid  must 
be  frequently  changed,  the  tissue  is  to  be  transferred  directly,  withozit 
previous  washing,  to  150  c.c.  of  70  per  cent,  alcohol  and  on  the  follow- 
ing day  to  the  same  quantity  of  90  per  cent,  alcohol.  The  bottle  con- 
taining the  tissue  must  be  placed  in  the  dark  (p.  35),  and  the  alcohol  fre- 
quently changed  during  the  first  eight  days.      Sections  may  then  be  made. 


THE    NERVOUS    SYSTEM.  23  I 

The  sections  are  to  be  placed  in  a  capsule  containing  20  c.c.  of  70 
per  cent,  alcohol  and  as  soon  as  possible  transferred  from  this  to  30  c.c. 
of  Weigert's  hematoxylin  to  which  i  c.c.  of  lithium  carbonate  solution 
has  been  added  (p.  24).  In  five  or  six  hours  the  now  very  dark,  untrans- 
parent  sections  should  be  transferred  to  50  c.c.  of  distilled  water  plus  i  c.c. 
of  lithium  carbonate  solution.  In  a  half-hour,  during  which  time  the 
fluid  must  be  changed  several  times,  the  sections  will  give  off  no  more 
color  and  are  then  to  be  placed  in  30  c.c.  of  potassium  permanganate 
solution  for  differentiation  (p.  24).  In  from  one-half  to  three  minutes 
they  are  to  be  washed  for  one  minute  in  distilled  water  and  then  trans- 
ferred to  20  c.c.  of  the  acid  mixture  (p.  24).  The  capsule  containing 
the  acid  mixture  should  be  covered.  The  decolorization  occurs  in  from 
ten  to  fifty  seconds  ;  the  gray  substance  becomes  light  yellow,  almost 
white,  the  white  substance  (the  medullated  nerve-fibers)  appears  very 
dark.  (Very  often  the  colored  blood-cells  are  also  stained  a  dark  color, 
which  is  explained  by  the  fact  that  they  contain  substances  that  are  also 
contained  in  the  myelin.)  Now  transfer  the  sections  to  a  capsule  con- 
taining 30  c.c.  of  distilled  water  and  in  five  minutes  to  a  second  capsule 
containing  the  same  quantity  of  fresh  distilled  water,  in  which  they  may 
remain  for  two  or  three  days,  the  water  meanwhile  to  be  frequently 
changed  (even  running  water  may  be  used).  Then  they  are  put  into 
10  c.c.  of  alum-carmine,  in  which  they  may  remain  from  three  to  fifteen 
hours.  Mount  in  xylol-balsam.  The  alum-carmine  staining  may  be 
omitted. 

The  foregoing  directions  are  intended  for  thin,  well-fixed  prepara- 
tions. If  the  sections  are  thick,  if  the  tissue  has  lain  a  long  time  in 
alcohol,  more  time  will  be  required  for  staining  and  reduction.  Should 
the  staining  be  unsuccessful,  place  unstained  sections  in  Miiller's  fluid 
for  twenty-four  hours,  wash  one  minute  in  distilled  water,  then  stain, 
and  satisfactory  results  may  be  obtained.  Should  the  decolorization  be 
insufficient,  if  the  gray  substance  does  not  become  yellowish-white,  the 
procedure  should  be  repeated  ;  that  is,  the  sections  are  to  be  again  placed 
in  distilled  water  one  minute,  then  in  potassium  permanganate  one  or 
two  minutes,  then  in  distilled  water  one  minute,  and  finally  in  the  acid 
mixture.  The  given  quantities  of  the  permanganate  solution  and  of  the 
acid  mixture  are  sufficient  for  only  about  20  sections.  If  it  is  desired  to 
treat  more  sections  larger  quantities  of  these  fluids  must  be  used. 

No.  75. — Tlie  spinal  cord ;  staining  of  axis- cylinders  and  of  cells. — 
Place  pieces  at  the  most  2  cm.  long  in  200  c.c.  of  Miiller's  fluid,  that 
must  be  changed  daily  during  the  first  week  and  once  a  week  thereafter. 
In  four  weeks  transfer  the  pieces  directly  from  Miiller's  fluid  to  about 
50  c.c.  of  sodium  carminate  (i  per  cent,  aqueous  solution),  in  which  they 
should  remain  for  three  days.  Dnring  this  time  the  bottle  containing  the 
pieces  must  be  frequently  shaken.  The  stained  pieces  are  to  be  washed 
for  twenty-four  hours  in  running  water,  then  placed  in  150  c.c.  of  70 
per  cent,  alcohol,  and  after  five  hours  transferred  to  the  same  quantity 
of  95  per  cent,  alcohol.  Mount  the  cross-sections  in  xylol-balsam 
(Fig.   122). 


232 


HISTOLOGY. 


No.  76. — Spinal  cord,  after  Golgi.'^ — Remove  the  spinal  cord  along 
with  the  (still  cartilaginous)  vertebral  column  of  newborn  rats  or  mice 
and  treat  them  according  to  the  method  described  on  page  45.  The 
length  of  time  the  objects  should  remain  in  the  Golgi  mixture  depends 
upon  the  elements  it  is  desired  to  impregnate. f      It  requires  from 

Two  to  three  days  for  neuroglia  cells, 

Three  to  five  days  for  nerve-cells, 

Five  to  seven  days  for  nerve-fibers  (collaterals). 

Since  the  pieces  must  be  used  as  soon  as  they  are  taken  out  of  the 
silver  solution  only  one  piece  at  a  time  should  be  transferred  to  the 
absolute  alcohol.  Cut  the  sections  through  spinal  cord  and  vertebral 
column. 

The  spinal  cord  of  a  three-  or  seven-day-old  embryo  chick  furnishes 
still  better  results,  but  it  is  necessary  to  embed  the  tissue  in  celloidin 
(see  Microtome  Technic).  The  spinal  cord  of  kittens,  as  well  as  that  of 
human  embryos  from  20  to  40  cm.  long,  yields  very  useful  results. 

No.  yj. —  TJie  brain;  staining  of  medidlated  nerve-fibers. — Apply  the 
method  given  in  No.  74.  If  an  entire  human  brain  is  to  be  placed  in 
Miiller's  fluid,  many  deep  incisions  should  be  made  in  it  and  about  3 
liters  of  the  fixing  fluid  should  be  used. 

No.  78. — The  brain  ;  cells. — Treat  pieces  i  or  2  cm.  square  of  the 
cerebral    cortex   (central  convolution)  and  of  the  cerebellar  cortex   like 

No.  75.  In  the  cerebral  cortex,  in  addition 
to  the  cell-forms  described,  an  extremely 
variable  number  of  vesicular  cavities  con- 
taining remnants  of  cells  (protoplasm  and 
nucleus)  may  be  seen  (Fig.  158,  z);  they 
are  probably  pericellular  lymph-spaces, 
which  by  post-mortem  alteration  of  the 
brain  substance  and  the  influence  of  the 
fixation  medium  have  become  abnormally 
enlarged.  The  sections  through  the  cere- 
bellar cortex  must  be  made  transverse  to 
the  long  axis  of  the  convolutions,  since 
the  ramifications  of  the  cells  of  Purkinje 
extend  only  in  planes  transverse  to  the  convolution.  Only  a  few^  cells 
of  Purkinje  lie  in  the  depths  of  the  convolutions. 

No.  79. — The  brain,  after  Golgi. ~^' — {ci)  For  a  topographic  vieiv, 
treat  the  brain   of  a   newborn   rat  or  mouse   in    the  unopened   cranium 


;.  158. — Portion  of  a  Section  of 
Human  Cerebral  Cortex.  X 
240.  p.  Small  pyramidal  cells;  a, 
the  nerve-process  of  a  pyramidal 
cell. 


*  Editor^ s  remark:  The  application  of  the  Cox- Golgi  mixture,  in  the  manner  described 
on  p.  45,  foot-note,  is  also  highly  recommended.  Since  it  can  be  applied  with  good  results  to 
the  central  nervous  system  of  adult  animals  it  offers  in  the  manipulation  of  the  material  and 
the  preparation  of  the  sections  valuable  advantages,  particularly  to  the  beginner.  After  the 
treatment  with  alcohol  the  larger  pieces  can  be  easily  cut  freehand  without  being  embedded, 
when  thick  sections  are  desired. 

f  If  the  action  of  the  mixture  is  too  brief  the  central  portions  of  the  sections  appear 
untransparent  and  are  penetrated  by  abundant  precipitates  ;  if  the  action  of  the  mixture  is  too 
prolonged  the  resulting  impregnation  of  the  elements  will  be  unsatisfactory. 


THE    NERVOUS    SYSTEM.  233 

according  to  the  method  gi\en  in  No.  76.      The   cranium  may  be  sec- 
tioned with  the  brain-substance. 

[b)  For  specimens  of  the  cortex  the  brain  of  a  mouse  from  eight  to 
thirty  days  old  is  most  suitable,  treated  with  the  Golgi  mixture  for  from 
two  to  three  days,  or  of  a  one-  to  fifteen-day-old-rabbit  or  a  kitten  under 
six  weeks  old,  treated  with  the  Golgi  mixture  for  fi\'e  days.  Pieces  of 
the  brain  of  adults  must  remain  in  the  Golgi  mixture  for  from  eight  to 
fifteen  days.      Further  treatment  like  No.  yG. 

No.  80. — The  cortex  of  the  cerebelliun,  after  Golgi.'' — Remove  the 
cerebellum  from  the  cranium  of  a  newborn  guinea-pig  (or  a  kitten  less 
than  six  weeks  old)  and  treat  it  according  to  the  method  given  in  No. 
jG.  The  staining  of  the  elements  of  the  cerebellum  is  more  difficult  to 
accomplish  than  of  those  of  the  cerebrum  and  the  spinal  cord.  Fail- 
ures are  frequent.  The  sections  should  be  principally  made  vertically 
to  the  long  axis  of  the  convolutions.  (For  embedding,  see  Microtome 
Technic.) 

No.  81. — Hypophysis  cerebri. — Treat  like  No.  86. 

No.  82. — Brain-sand  {acervnhis  cerebri). — Tease  the  epiphysis  in  a 
drop  of  salt  solution.  If  much  brain-sand  is  present  a  grating  sound 
will  be  heard  on  teasing  and  the  larger  concretions  can  be  seen  by  the 
unaided  eye.  Examine  with  the  low  power,  without  a  cover-glass  (Fig. 
135)  ;  the  granules  are  not  always  round,  but  often  oval  and  dentated  ; 
occasionally  the  irregularity  of  the  surface  is  indistinct,  because  the 
granules  are  enveloped  in  concentrically  arranged  connectiv^e-tissue 
fibers.  Push  aside  the  larger  granules  with  a  needle,  cover  a  few  of  the 
smaller  ones  with  a  cover-glass  and  treat  with  2  or  3  drops  of  hydro- 
chloric acid  (p.  53).  Bubbles  of  gas  develop  and  the  sharp  outlines  of 
the  granules  disappear. 

No.  83. — Corpnscula  aniylacea. — Select  the  brains  of  elderly  indi- 
viduals. With  a  scalpel  scrape  the  mesial  surface — that  directed  toward 
the  third  ventricle — of  the  optic  thalamus  and  distribute  the  scrapings 
with  a  needle  in  a  drop  of  salt  solution  ;  apply  a  cover-glass.  The 
corpuscles  are  easily  found,  and  are  recognized  by  their  bluish-green 
color  and  their  stratification  (Fig.  136,  ct).  They  must  not  be.  confused 
with  drops  of  extruded  myelin  (//),  which  are  always  clear  and  ha\e 
only  a  double  contour.  In  addition  there  are  found  in  such  preparations 
numerous  red  blood  corpuscles,  ependymal  cells  {d),  medullated  nerve- 
fibers,  differing  in  thickness,  and  ganglion  cells  ;  the  latter  are  \'ery  pale 
and  often  can  be  detected  only  by  their  pigmentation  (/).  Human 
brains,  even  though  not  absolutely  fresh,  are  still  useful. 

No.  84. — {(.i)  Spread  out  a  piece  i  cm.  long  of  the  choroid  plexus  in 
a  drop  of  salt  solution  and  apply  a  cover-glass.  The  convoluted  red 
blood-vessels  and  the  epithelium  of  the  plexus  can  be  seen. 

*  For  the  application  of  the  Cox-Golgi  mixture  see  p.  45  and  p.  232.  remark  *. 


t  t    1 

o4 


HISTOLOGY. 


(d)  Very  pretty  permanent  preparations  can  be  obtained  as  follows  : 
Carefully  spread  out  a  little  piece  of  the  plexus  in  salt  solution  ;  if  good 
fields  are  visible  with  the  low  power  let  the  salt  solution  flow  off"  and  add 
a  few  drops  of  Zenker's  fluid  (p.  21)  ;  then  apply  a  cover-glass,  at  the 
edge  of  which  place  a  little  more  of  the  Zenker's  fluid.  After  thirty 
minutes  displace  this  fluid  by  distilled  water,  and  after  another  thirty 
minutes  the  water  by  50  per  cent,  alcohol  to  which  a  few  drops  of  tinc- 
ture of  iodin  have  been  added.  In  fifteen  minutes  take  off  the  cover- 
glass  and  transfer  the  now  fixed  preparation  to  a  watch-glass  with  fresh 
50  per  cent,  iodin-alcohol,  to  which,  in  case  it  becomes  rapidly  decolor- 
ized, tincture  of  iodin  is  to  be  added.  In  from  fifteen  to  thirty  minutes 
transfer  the  object  to  pure  70  per  cent,  alcohol,  and  after  about  twelve 
hours  stain  it  with  hematoxylin  and  eosin  (p.  39,  3  d)  and  mount  in 
xylol-balsam  (p.  50). 


Epineurium. 


^^  Perineurium. 


Endoneurium. 


No.  85. — Transverse  sections  of  nerve-fiber  htndles. — Treat  a  piece  of 
nerve,  e.  g.  the  sciatic,  if  possible  of  man,  that  possesses  a  well-devel- 
oped  endoneurium,  according  to  the  method  given  in  No.    34,  p.  123. 

Place  it  for  six 
days  in  a  o.  i  per 
cent,  solution  of 
chromic  acid, 
then  wash  it  for 
from  three  to  four 
hours  in  running 
water,  and  hard- 
en it  in  gradually 
strengthened  al- 
cohols. When  the 
hardening  is  com- 
pleted cut  thin 
sections  with  a 
sharp  razor.  It  is 
advisable  to  em- 
bed the  tissue  in 
liver,  better  still, 
in  elder-pith  or  in 

the  pith  of  the  sunflower.  For  this  purpose  make  a  hole  in  the  dry  elder- 
pith  with  a  needle  and  then  carefully  insert  the  nerve.  Place  the  whole 
for  about  a  half  hour  in  water  ;  in  this  pith  swells  and  firmly  clasps  the 
nerve.  Stain  the  sections  in  picrocarmine  and  mount  in  glycerol.  The 
length  of  time  required  for  staining  varies  greatly.  The  sections  must 
be  very  carefully  handled  and  pressure  with  the  cover-glass  must  be 
scrupulously  avoided,  lest  the  sections  of  the  fibers,  which  are  not  disks 
but  short  cylinders,  be  turned  on  their  sides  and  not  a  fiber  in  section 
be  seen.  If  successful  the  section  will  show  the  somewhat  shrunken 
axis-cylinder,  resembling  a  red  nucleus,  surrounded  by  the  yellow  me- 
dulla, which  is  enclosed  by  the  reddish  neurilemma  and  the  fiber-sheath. 


Fig.  159. — From  a  Transverse  Section  of  a  Peripheral  (Spinal)  Nerve 
OF  A  Rabbit.  X  50.  In  the  lower  bundle,  on  the  right,  some  of  the 
transverse  sections  of  nerve-fibers  have  fallen  out,  others  are  lying  on 
their  side,  as  a  consequence  of  pressure.  In  the  rabbit  the  endoneu- 
rium is  only  slightly  developed. 


THE    NERVOUS    SYSTEM.  235 

The  cross-section  of  the  nerve-fiber  has  been  compared  to  a  picture  of 
the  sun  {Sonnoibildclicnfigiir^  (Fig.  i  59). 

No.  86. — Spinal  ganglia. — These  are  very  inaccessible.  Therefore 
remove  the  Gasserian  ganghon  from  the  depression  in  which  it  is  lodged, 
on  the  anterior  surface  of  the  petrous  portion  of  the  temporal  bone,  and 
place  it  in  about  100  c.c.  of  Miiller's  fluid  for  fixation.  After  four  weeks 
wash  it  for  three  hours  in  running  water  and  harden  it  in  50  c.c.  of  grad- 
ually strengthened  alcohols  (p.  35).  Cut  the  thinnest  possible  transverse 
and  longitudinal  sections  ;  stain  them  thirty  seconds  in  hematoxylin, 
then  from  two  to  five  minutes  in  eosin  (p.  39,  3  b),  and  mount  in  xylol- 
balsam.  The  ganglion  cells  are  pale  red  ;  the  axis-cylinders  deep  red  ; 
the  medullary  sheaths  brownish  ;  the  nuclei  blue  (Fig.  141).  If  the 
section  is  not  sufficiently  thin  the  large  number  of  deeply-stained  nuclei 
will  render  it  difficult  to  see  the  other  structures.  For  this  reason  it  is 
better  to  stain  the  thick  sections  in  picrocarmine  for  two  or  three  days 
and  mount  them  in  xylol-balsam.  The  nuclei  are  then  not  so  intensely 
stained.  Occasionally  the  protoplasm  of  the  ganglion  cell  contracts 
and  thus  acquires  a  stellate  outline  (Fig.  141,  x),  that  may  easily  lead 
the  beginner  to  confuse  it  with  a  multipolar  ganglion  cell. 

T-shaped  branches  may  be  seen  in  preparations  of  the  spinal  cord 
treated  after  No.  76.  In  young  embryo  chicks  the  spinal  ganglion 
cells  are  still  bipolar  ;  unipolar  cells  are  found  in  embryo  chicks  about 
seventeen  days  old.  Transition  forms  occur  in  chick  embryos  between 
the  ninth  and  fourteenth  days  and  in  embryo  rabbits  from  5  to  12  cm. 
long.      Staining  with  methylene  blue  (p.  42)  is  strongly  recommended. 

No.  "^J. — Sympathetic  ganglia. — Fix  and  harden  the  large  superior 
cervical  ganglion  of  the  sympathetic  nerve  like  No.  ?>6.  Here,  too,  on 
account  of  the  abundance  of  nuclei  nuclear  staining  is  applicable  only  to 
very  thin  sections.  The  characteristic  bundles  of  nonmedullated  nerve- 
fibers,  cut  obliquely  and  transversely,  can  be  recognized  with  the  low 
power  ;  the  ganglion  cells  are  also  distinct,  but  their  processes  are  very 
unsatisfactory  and  often  cannot  be  detected  ;  the  latter  may  be  better 
exhibited  according  to  the  method  given  in  No.  76  and  a  suitable  object 
is  the  cervqcal  portion  of  a  ten  or  fifteen-day-old  embryo  chick,  while 
still  better  results  are  obtained  by  staining  with  methylene  blue  (p.  42). 
The  intestine  of  infants  (ganglia  of  the  myenteric  plexus)  is  also  useful. 
See  further  Dogiel  (Arch,  f  Anat.  und  Physiol.  Anatom.,  1899,  p.  135). 

No.  ^d>. — Simple  tactile  cells;  intraepithelial  nerve-fibers ;  cells  of 
Langerhans  ;  tactile  corpuscles. — Prepare  a  mixture  of  gold  chlorid  and 
formic  acid  (p.  47),  boil  it  and  let  it  cool  ;  then  cut  from  the  volar  side 
of  a  freshly  amputated  finger  or  toe  (with  scissors  applied  flatwise)  sev- 
eral small  pieces  of  the  epidermis  and  uppermost  layers  of  the  corium 
about  5  mm.  square  and  i  mm.  thick.  Carefully  remove  any  fat  attached 
to  the  under  surface  of  the  corium  and  place  the  pieces  in  the  gold  and 
formic  acid  mixture  for  one  hour,  in  the  dark.  Then,  with  glass  rods, 
transfer  the  pieces  to  lo  c.c.  of  distilled  water  and  in  a  few  minutes  to 


236  HISTOLOGY. 

fresh  distilled  water  to  which  formic  acid  has  been  added  (p.  47),  and 
expose  the  whole  to  daylight  (sunlight  is  unnecessary).  In  from  twenty- 
four  to  forty-eight  hours  the  objects  have  become  dark  violet.  They  are 
now  to  be  hardened  in  30  c.c.  of  gradually  strengthened  alcohols.  In 
eight  days  the  pieces  may  be  embedded  in  liver  and  sectioned  ;  mount 
in  xylol-balsam.  The  epidermis  is  red-violet  in  different  tints  ;  the  nuclei 
are  only  to  be  seen  in  places  and  often  are  wholly  imperceptible  ;  the 
corium  is  white  ;  the  capillaries,  the  excretory  ducts  of  the  coil-glands, 
and  the  nerves  are  dark  violet  to  black.  For  simple  tactile  cells  the 
thinnest  possible  sections  are  necessary.  They  may  often  be  found 
near  the  excretory  ducts  of  the  coil-glands  (Fig.  145).  Care  must  be 
taken  not  to  confuse  them  with  nuclei  of  shrunken  epithelial  cells. 

The  intraepithelial  nerve-fibers  appear  as  delicate  filaments  ;  their 
connection  with  the  nerve-fibers  in  the  corium  is  difficult  to  trace.  Pro- 
cesses of  the  cells  of  Langerhans,  in  thin  sections,  are  apt  to  be  con- 
fused with  the  intraepithelial  nerve-fibers  (Fig.  144). 

The  cells  of  Langerhans  and  the  tactile  corpuscles  are  easily  seen  ; 
in  thick  sections  the  tactile  corpuscles  are  black  (Fig.  144),  in  thin  sec- 
tions red-violet  (Fig.  149). 

No.  89. — Compound  tactile  cells. — Cut  the  yellowish  wax-like  skin, 
or  cere,  from  the  lateral  edges  of  the  upper  beak  of  a  duck  or  goose  and 
treat  pieces  i  or  2  mm.  thick  and  i  cm.  long  with  3  c.c.  of  2  per  cent, 
osmic-acid  solution  plus  3  c.c.  of  distilled  water  ;  place  the  whole  in  the 
dark  from  eighteen  to  twenty-four  hours  ;  then  wash  the  pieces  for  one 
hour  in  running  water  and  transfer  them  to  20  c.c.  of  90  per  cent,  alco- 
hol. In  six  hours  the  objects  may  be  sectioned.  Embed  them  in  liver 
and  make  the  sections  from  the  corium  toward  the  epithelium,  not  the 
reverse.  The  sections  may  be  mounted  unstained  in  xylol-balsam.  The 
olive-green  tactile  cells  can  be  readily  seen,  but  the  entrance  of  the 
nerve-fiber  is  difficult  to  find  (Fig.  146).  In  addition  Herbst's  cor- 
puscles occur  in  the  sections  (p.  224).  If  it  is  desired  to  stain  the  sec- 
tions, use  a  nuclear  staining  solution  (p.  38). 

No.  90. — Cylindrical  end-lndbs. — With  scissors  and  forceps  cut  from 
the  fresh  eye  of  a  calf  pieces  i  cm.  square  of  the  scleral  conjunctiva,  up 
to  the  corneal  margin,  taking  care  not  to  roll  them.  It  is  better  to  let 
them  lie  on  the  sclera  until  all  are  cut.  Carefully  slip  the  pieces,  epi- 
thelial side  up,  from  the  sclera  on  to  a  cork  plate  and  span  them  out  with 
needles.  Moisten  the  surface  with  a  few  drops  of  the  vitreous  humor 
obtained  from  the  eye  ;  with  fine  scissors  and  forceps  dissect  off  a  thin 
membrane  consisting  of  a  thin  layer  of  connective  tissue  and  the  epithe- 
lium resting  upon  it.  This  operation  must  be  done  with  great  care  ; 
folding  and  torsion  of  the  membrane  must  as  far  as  possible  be  avoided. 
The  membrane,  with  the  epithelial  side  up,  should  now  be  slipped  on  to 
a  dry  slide  and  spread  out.  At  first  it  will  draw  together,  but  in  a  mo- 
ment or  two  the  edges  dry  somewhat  and  adhere  to  the  glass  and  it  can 
then  be  extended  without  much  difficulty.  The  slide  with  the  prepa- 
ration is  to  be  placed  in  a  glass  jar  containing  65  c.c.  of  distilled  water  to 


THE    NERVOUS    SYSTEM.  237 

which  2  c.c.  of  acetic  acid  have  been  added.  In  about  an  hour  (or  later), 
during  which  time  the  membrane  swells  considerably  and  floats  from  the 
slide,  by  carefully  touching  it  with  a  clean  needle  endeavor  to  remove  the 
epithelium  ;  it  loosens  without  much  trouble  and  floats  off  in  fine  white 
shreds.  If  this  is  not  done  cautiously  the  end-bulbs  lying  close  beneath 
the  epithelium  may  be  torn  off  with  it.  The  more  thoroughly  the  epithe- 
lium is  removed  the  better.  After  it  has  lain  four  or  five  hours  in  the 
dilute  acetic  acid  transfer  the  swollen  piece  with  a  few  drops  of  the  same 
fluid  to  a  slide,  apply  a  cover-glass  and  make  slight  pressure  upon  it 
with  the  outspread  branches  of  the  forceps.  On  examination  with  the 
low  power  the  blood-vessels  are  plainly  seen — they  are  recognized  by 
their  distinct  nuclei — and  also  the  medullated  nerve-fibers.*  Trace  such 
a  fiber  until  the  medulla  ceases  ;  examine  this  point  with  the  high  power, 
for  there  the  end-bulbs  are  most  apt  to  be  found.  In  many  cases  noth- 
ing will  be  seen  but  numerous  nuclei  and  even  when  a  favorable  situation 
is  found  the  end-bulbs  are  so  pale  that  it  is  very  difficult  to  perceive 
them  (Fig.  147)  ;  the  axis-cylinder,  too,  is  often  very  difficult  to  detect. 
Only  the  practised  microscopist  will  succeed  in  finding  them.  Beginners 
are  advised  not  to  attempt  this  preparation. 

No.  91. — Lamellar  corpuscles. — These  are  best  obtained  from  the 
mesentery  of  a  cat,  where  usually  they  can  be  seen  with  the  unaided  eye. 
They  appear  as  milky,  glass-like,  transparent,  oval  spots  between  the 
strands  of  the  adipose  tissue  of  the  mesentery.  Their  number  varies 
greatly.  Occasionally  they  are  very  scarce  and  of  such  small  size  that 
to  find  them  requires  close  searching.  Cut  out  the  portion  of  the  mes- 
entery containing  a  corpuscle,  and  spread  it  out  in  a  drop  of  salt  solution 
on  a  slide  lying  on  a  black  background.  Endeavor  to  remove  the 
attached  clusters  of  fat-cells,  taking  care  not  to  prick  the  corpuscle. 
Ascertain  with  a  low  power,  without  a  cover-glass,  whether  the  corpus- 
cle has  been  sufficiendy  isolated  ;  then  cover  it  with  another  drop  of 
salt  solution  and  a  cover-glass.  Pressure  must  be  carefully  avoided. 
The  corpuscle  represented  in  figure  148  is  very  small. 

With  the  high  power  one  can  distinctly  see  the  nuclei  of  the  cells 
between  the  capsules  ;  the  oval  nuclei  of  the  inner  bulb  are  often  in- 
distinct and  pale.  If  it  is  desired  to  preserve  the  preparation,  treat  it 
under  the  cover-glass  with  i  or  2  drops  of  i  per  cent,  osmic  acid  and 
after  the  medulla  has  become  black  and  the  inner  bulb  has  become 
brown  displace  the  acid  with  very  dilute  glycerol.  Methylene  blue 
staining  (p.  42)  is  recommended.  See  further  Sokolow  (Anat.  Anzeiger, 
Bd.  XVI,  p.  453). 

No.  92. — Motor  nerve-endings. — {a)  Terminal  ramifications. — Pre- 
pare a  mixture  of  24  c.c.  of  i  per  cent,  gold  chlorid  solution  plus  6  c.c. 
of  formic  acid,  boil  it  and  let  it  cool  ;  cut  out  small  pieces  3  or  4  cm. 
long  of  the  intercostal  muscles  of  a  rabbit  and  treat  them  like  No.  88  ; 

*  In  the  calf  some  of  the  nerve-fibers  are  nonmedullated  ;  these  are  not  recommended 
for  the  investigation. 


238  HISTOLOGY. 

after  the  dark-violet  pieces  have  lain  from  three  to  six  days  in  70  per 
cent,  alcohol  tease  a  muscle-bundle  about  5  mm.  broad  in  a  drop  of 
dilute  glycerol  to  which  a  very  small  drop  of  formic  acid  has  been  added. 
It  is  of  advantage  to  make  slight  pressure  on  the  cover-glass.  To  find 
the  terminal  ramifications  trace  with  the  low  power  the  easily  recognized 
black  nerve-fibers  (Fig.  153).  The  addition  of  another  drop  of  acetic  or 
formic  acid  often  makes  the  picture  sharper. 

{p)  Nuclei  of  the  viotoj'  plate. — Place  the  anterior  halves  of  the  eye- 
muscles  of  a  recently  killed  rabbit  in  97  c.c.  of  distilled  water  plus  3  c.c. 
of  acetic  acid.  After  six  hours  transfer  the  muscles  to  distilled  water; 
with  the  scissors  cut  off  a  thin  flat  piece  and  spread  it  out  on  a  slide  ; 
the  ramifications  of  the  whitish  nerves  can  be  plainly  seen  with  the  un- 
aided eye.  With  low  magnification  (50  diameters),  the  anastomoses  of 
the  nerve -bundles,  as  well  as  the  blood-vessels,  that  are  easily  recognized 
by  the  transversely  placed  nuclei  of  their  smooth  muscle-fibers,  can  be 
seen.  On  account  of  the  large  number  of  sharply  contoured  nuclei  be- 
longing to  the  intramuscular  connective  tissue,  the  end-plates  are  not 
easy  to  find.  If  a  nerve-fiber  be  traced  it  will  soon  be  seen  that  the 
double-contoured  medullary  sheath  ceases  abruptly  and  loses  itself  in  a 
group  of  nuclei  ;  these  are  the  nuclei  of  the  motor  plate,  the  other  details 
of  which  are  not  distinctly  visible.  The  cross-striation  of  the  muscle- 
fibers,  which  are  very  pale,  is  often  indistinct  (Fig.   i  54). 

No.  93. —  The  suprarenal  bodies  ;  topographic  view. — Fix  the  entire 
suprarenal  body  of  a  child  in  200  c.c.  of  o.  i  per  cent,  chromic  acid  for 
eight  days  and  harden  it  in  150  c.c.  of  gradually  strengthened  alcohols  ; 
mount  unstained  sections  in  dilute  glycerol  (Fig.  ISS)- 

No.  94. — Elements  of  the  suprarenal  body. — Tease  portions  of  the 
fresh  organ  in  a  drop  of  salt  solution.  The  elements  are  very  delicate 
and  therefore  injured  cells  are  of  frequent  occurrence. 

No.  95. — For  the  study  of  the  minnte  structure  of  the  suprarenal 
body  place  2  cm.  cubes  of  the  fresh  organ  in  100  c.c.  of  Zenker's  fluid 
(p.  33)  and  after  from  twelve  to  twenty-four  hours  harden  in  an  equal 
quantity  of  gradually  strengthened  alcohols  ;  cut  thin  sections,  stain 
them  in  Hansen's  hematoxylin,  and  mount  in  xylol-balsam  (Fig.  157). 
For  the  exhibition  of  the  nerves  treatment  with  the  Golgi  mixture  for 
from  six  to  eight  days  and  with  the  0.75  per  cent,  silver  solution  for 
from  two  to  three  days,  with  several  repetitions  of  this  procedure, 
is  recommended. 


THE    DIGESTIVE    ORGANS.  239 

V.   THE   DIGESTIVE   ORGANS. 

The  Mucous  Membrane. 

The  inner  surface  of  the  entire  aHmentary  tract,  of  the  respiratory 
organs,  of  certain  parts  of  the  genito-urinary  system,  and  of  some  of  the 
organs  of  special  sense  is  covered  by  a  soft,  moist  membrane,  the  nmcotis 
membrane  or  tunica  mucosa.  It  is  composed  of  a  soft  epithehum  and  of 
connective-tissue.  Immediately  under  the  epithelium  is  a  structureless 
membrane,  the  membrana  propria  (p.  86) ;  beneath  this  follows  the 
tunica  propria  (stroma),  which  passes  by  a  gradual  transition  into  the 
subjacent,  loose-textured  tela  subuiucosa,  that  in  turn  connects  the  mucous 
membrane  with  the  underlying  structures,  for  example,  muscles  or 
bones.  The  epithelium  of  the  glands  is  derived  from  the  epithelium 
of  the  mucous  membrane  (see  p.  80). 

A.   HEADGUT. 

the  oral  cavity. 

The  Mucous  Membrane  of  the  Oral  Cavity. 
The  mucous  membrane  of  the  mouth  consists  of  three  parts  :  (i) 
the  epithelium,  (2)  the  tunica  propria,  and  (3)  the  submucosa  (Fig.  160). 
The  epithelium  is  typical  stratified  squamous  epitheliurn  (see  page  77). 
The  tunica  propria  is  formed  of  interlacing  connective-tissue  bundles 
richly  interspersed  with  elastic  fibers.  The  bundles  of  the  uppermost 
layers  are  very  slender  and  form  a  compact,  apparently  almost  homo- 
geneous felt-work.  The  surface  of  the  tunica  propria  is  beset  with 
numerous,  usually  simple  papillse  (Fig.  160,  i),  the  height  of  which  varies 
greatly  in  the  different  regions  of  the  oral  cavity.  The  highest  papillae 
(0.5  mm.)  occur  at  the  edge  of  the  lips  and  on  the  gums.  The  tunica 
propria  passes  without  sharp  limits  into  the  submucosa,  w4iich  consists  of 
somewhat  thicker  bundles  of  connective  tissue,  among  which  the  elastic 
fibers  are  not  numerous.  The  submucosa  is  in  general  loosely  attached 
to  the  walls  of  the  oral  cavity  ;  only  on  the  gums  and  on  the  hard 
palate  is  it  firmer  and  here  intimately  united  to  the  periosteum.  It  sup- 
ports the  ^/(^wrt'j- of  the  mucous  membrane;  with  the  exception  of  the 
sebaceous  glands  occasionally  found  at  the  edge  of  the  lips  and  on  the 
inner  surface  of  the  cheeks,  these  are  branched  alveolo-tubular  glands 
from  I  to  5  mm.  in  size.  Their  main  excretory  duct  (Fig.  160,  2)  is 
somewhat  expanded  at  its  lower  end  and  in  the  greater  part  of  its  length 
is  lined  with  stratified  squamous  epithelium  ;  the  branches  and  twigs  into 


240 


HISTOLOGY. 


which  it  divides  and  subdivides  are  lined  with  cyHnder  epitheHum,  the 
larger  branches  with  the  stratified  variety,  the  smaller  branches  with  the 
simple.  Not  infrequently  the  main  excretory  duct  receives  the  excretory 
tubes  of  small  accessory  mucous  glands  (Fig.  160,  3).  For  the  minute 
structure  of  the  end-pieces,  see  the  next  chapter.  The  numerous  blood- 
vessels of  the  oral  mucous  membrane  are  arranged  in  two  networks, 
situated  in  two  horizontal  planes,  of  which  the  coarser  lies  in  the  submu- 
cosa,  the  other,  finer,  in  the  tunica  propria.  From  the  latter  capillary 
loops  ascend  into  the  papillae.      The  lymph-vessels   similarly  form   two 


Epithelium. 


%    J  Tunica  propria. 


Submucosa 


Muscles. 


Fig.  160. — Vertical  Section  through  the  Mucous  Membrane  of  the  Lip  of  an  Adult  Man.  X  30. 
I.  Papilla ;  2,  excretory  duct ;  the  lumen  is  cut  at  only  one  point ;  3,  accessory  gland  ;  4,  a  branch  of 
the  excretory  duct  in  transverse  section  ;  5,  gland  bodies  grouped  into  lobules  by  connective  tissue ; 
6,  a  gland-tubule  in  transverse  section.     Technic  No.  97. 

networks,  a  wide  in  the  submucosa,  a  narrow  in  the  tunica  propria.  The 
medullated  nerve-fibers  form  a  wide-meshed  reticulum  in  the  submucosa, 
from  which  many  ramifying  fibers  ascend  to  the  tunica  propria.  Here 
they  terminate  in  end-bulbs  (p.  222),  or  they  lose  their  medullary  sheath 
and  as  nonmedullated  nerve-fibers  penetrate  into  the  epithelium  and 
after  repeated  division  terminate  there  in  free  endings. 


The  Glands  of  the  Oral  Cavity. 

The  gland-cells  of  the  oral  cavity  are  of  two  kinds  :  (i)  cells  that 
yield  a  secretion  rich  in  albumin,  albinninoiis  or  serous  cells ;  (2)  cells 
that  produce  a  secretion  consisting  of  mucin,  nuicoiis  or  imicin  cells. 


THE    DIGESTIVE    ORGANS. 


241 


The  serous  cells,  examined  when  fresh,  are  characterized  by  numer- 
ous highly  refractive  granules.  In  fixed  preparations  they  appear  some- 
times dark  and  of  shght  circumference  (empty  stage),  sometimes  a  trifle 
clearer  and  larger  (loaded  stage),  in  correspondence  with  the  functional 
state  (cf.  Fig.  24,  p.  80).  The  spheric  nucleus  is  situated  not  quite  in  the 
cell  center,  usually  nearer  the  cell  base. 

The  mucous  cells  in  the  fresh  state  are  much  less  refractive.  In 
fixed  preparations  the  typical  mucous  *  cells  appear  clear  ;  when  they 
are  filled  with  secretion  the  nucleus  is  flattened  and  lies  pressed  against 
the  cell  base  and  when  the  contents  are  discharged  it  merely  becomes 
oval,  without  essential  change  in  place  and  position.  The  elaborated 
secretion  (not  the  granular  precursors  of  the  same)  can  be  stained  by 
many  anilin  pigments,  also  by  Delafield's  hematoxylin  and  by  mucicar- 
mine  {cf.  e.  g.  Fig.  25). 


Man. 


Man. 


Mucous  glands. 


Serous  glands. 


Fig.  161. — Fro.m  Sections  of  Lingual  Glands.  I.  Tubule  in  cross-section  with  {b)  gland-cells  empty 
of  secretion  and  (c)  gland-cells  filled  with  secretion  ;  rf,  lumen.  II.  Tubule  in  cross-section  in  which 
ail  the  cells  are  filled  with  secretion.  III.  Cross-section  of  a  mucous  gland-tubule.  I\'.  Several  tub- 
ules of  a  serous  gland  ;  at  d  the  very  small  lumen.  V.  Tubules  with  a  large  (rf)  and  a  small  {d')  lumen. 
All  the  sections  are  magnified  240  times.     Technic  No.  102. 

Only  a  few  glands  of  the  oral  cavdty  of  man  contain  exclusively 
one  kind  of  cells  ;  to  these  belongs  the  parotid  gland,  the  end-pieces  of 
which  are  constructed  entirely  of  serous  cells,  also  the  "  serous  lingual 
glands  "  situated  in  the  region  of  the  foliate  and  the  vallate  papillse.  The 
glands  of  the  anterior  surface  of  the  soft  and  of  the  hard  palate,  also  the 
"  mucous  glands"  of  the  root  of  the  human  tongue,  contain  exclusively 
typical  mucous  cells.  All  other  glands  of  the  oral  cavity  are  "  mixed 
glands,"  and  mixed  in  such  manner  that  some  end-pieces  are  clothed  by 


*  By  this  name  I  would  designate  those  mucous  cells  the  cell-body  of  which  has  for  the 
greater  part  become  a  collecting  center  for  secretion  (p.  81)  and  which  in  different  functional 
phases  long  retains  substantially  this  center  within  its  circumference.  Not  all  mucous  cells 
share  this  properly  ;  the  collecting  center  of  the  human  olfactory  glands  is  very  small  and  in 
normal  circumstances  appears  not  greatly  to  enlarge  ;  in  the  mucous  cells  of  the  gastric  epithe- 
lium, also  in  those  of  the  lingual  glands  of  the  cat,  the  dimensions  of  the  collecting  center  vary 
very  considerably,  according  to  the  phase  of  the  functional  cycle. 
16 


242 


HISTOLOGY. 


serous  cells  only,  while  other  end-pieces  contain  chiefly  mucous  cells, 
between  which  single  or  groups  of  serous  gland-cells  are  situated.  These 
latter,  where  their  lateral  surfaces  are  in  contact  with  mucous  cells,  are 
subjected  to  compression  and  may  be  indeed  apparently  entirely*  pushed 
back  from  the  axial  gland  lumen  and  then  form  the  "demilunes"  of 
Giannuzzi  t  ("border-cells"). 

Hereby  for  the  present  I  accept  this  interpretation  of  many  demilunes,  as 
serous  gland-cells,  (i)  because  they  contain  granules  like  those  of  the  serous 
gland-cells,  (2)  because  of  their  peculiar  relations  to  the  secretory  capillaries, 
and  (3)  because  normally  differences  between  them  and  the  mucous  cells, 
even  in  varying  functional  states,  are  demonstrable.  Whether,  on  the  other 
hand,  all  demilune  cells  are  of  serous  nature,  is  very  doubtful.  Empty  mucous 
cells,  particularly  those  with  collecting  centers  of  variable  size,  may  be  pushed 

from  the  lumen  by  neighbors  filled  with 
secretion  and  so  become  demilunes. 

Accordingly  we  classify  the 
glands  of  the  oral  cavity  as  pure 
serous,  pure  mucous,  and  mixed 
p-lands. 


Intercellular  secretory 
capillaries,  jj 


SEROUS 


GLANDS  OF 
CAVITY. 


THE  ORAL 


I.  The  serous  lingual  glands 
(Ebner's  glands)  are  compound  tu- 
bular glands  ;  their  aqueous  ("  se- 
rous ")  secretion  is  marked  by  its 
high  content  of  albumin,  hence  the 
name  "albuminous  glands," 

These  serous  glands  are  con- 
fined to  the   region   of  the  vallate 
and  foliate  papillae  ;  their  excretory 
ducts  open,  as  a  rule,  in  the  furrows 
between  papilla  and  wall    (Fig.    185)  and    are  clothed  in  a  simple  or 
stratified — not  rarely  ciliated — cylinder  epithelium  ;    the  small  tubules 
consist  of  a  delicate   membrana  propria  and  short  cylindric  or  conical, 


Fig.  162. — From  a  Section  of  the  Root  of  the 
Tongue  of  a  Mouse.  X  240.  A  serous  gland 
with  _  its  tubular  system  blackened  by  Golgi's 
reaction.  The  tubular  character  is  easily  recog- 
nized. The  right-hand  lower  portion  of  the  gland 
is  completed  by  the  schematic  sketching  in  of 
the  cells.    Technic  No.  126. 


*  In  reality  they  stand  in  communication  with  the  lumen  through  a  secretory  capillary 
{cf.  p.  86). 

f  Not  to  be  confused  with  these  are  the  so-called  demilunes  of  Pfliiger,  which  are  formed 
by  those  mucous  cells  in  which  the  peripheral  protoplasmic  division  is  not  entirely  filled.  They 
are  particularly  fine  in  the  lingual  glands  of  the  cat.  Oblique  sections  of  the  membrana  propria 
and  the  stellate  cells  lying  upon  it  may  give  rise  to  deceptive  pictures,  resembling  the  demi- 
lunes. 


THE    DIGESTIVE    ORGANS. 


243 


membrane-less  cells,  which  in  man  and  sheep  exhibit  two  zones  :  an 
inner  dark,  beset  with  fine  granules,  and  an  outer  clear  zone,  that  encloses 
the  round  nucleus.*  The  axial  lumen  of  the  tubules  (especially  in  ani- 
mals) is  very  narrow  (Fig.  161,  d  d'),  and  takes  up  still  narrower  inter- 
cellular secretory  capillaries  (Fig.  162). 

2.  T\\Q.  parotid  gla]id  {^■An(\\x\-d.  parotis,  auricular  salivary  gland)  is 
preeminently  a  compound  alveolar  gland  (p.  85)  and  of  .all  the  oral  salivary 
glands  possesses  the  most  highly  differentiated  duct  system  ;  the  branches 
of  the  excretory  duct  pass  into  well-developed  salivary  tubes,  that  con- 


Fat-cells 


End-piece 
Excretory 
duct. 


_     ^^r\      , — •■^■c.,<v. 


^^V 


<l 


Secretory  '  , 

tube.  ':    '         :,  '   :  .  "  -^-1 


m- 


Intercalated       ,  ,        i  .    , 
Intercalated 


piece. 


hnd-pieces.  ,-,,-.  ^        ,   ,  ,   -   ~'^ S 


piece. 


Fig.  163. — Scheme  of  the  Human       Fig.  164. — Section  of  the  Parotid  Gland  of  Adult  Man.      X  252. 
Parotid  Gland.  The  very  narrow  lumina  are  entirely  invisible  in  this  preparation. 

Technic  No.  118. 

tinue  in  long,  narrow  intercalated  divisions.  The  latter  lead  into  short, 
simple  or  branched  end-pieces  (Fig.  163).  The  excretory  duct,  parotid 
duct  (Stenoni),  characterized  by  a  broad  membrana  propria  lying  imme- 
diately beneath  the  epithelium,  is  clothed  in  a  two-layered  epithelium, 
here  and  there  intermixed  with  goblet  cells,  that  gradually  becomes  one- 
layered  in  the  smaller  branches.  The  tall  cylindric  epithelial  cells  of  the 
secretory  tubes  show  distinct  longitudinal    striation   at  their  base  icf.  p. 

*  These  differences  can  be  brought  out  only  by  special  methods  and  high  magnification. 
The  figure  i6i  shows  nothing  of  this.  In  the  horse,  pig,  and  cat  the  two  zones  are  in  general 
indistinct,  in  the  rabbit  not  present.  Occasionally  between  the  serous  tubules  are  found  a  few 
tubules  containing  some  mucous  and  some  serous  cells.  In  the  cat  the  other  lingual  glands 
also  are  of  mixed  nature. 


244 


HISTOLOGY. 


88),  the  intercalated  pieces  (Fig.  164)  are  clothed  with  very  slender, 
often  spindle-shaped  cells.  Finally,  the  end-pieces  consist  of  a  delicate 
membrana  propria  with  stellate  cells  and  of  cubical  serous  gland-cells  ; 
in  the  empty  state  these  are  small  and  dimly  granular,  in  the  loaded 
state  larger  and  somewhat  clearer.  {^Cf.  p.  80.)  Free-ending,  simple 
secretory  capillaries  extend  from  the  axial  lumen  between  the  gland- 
cells,  without  reaching  the  membrana  propria. 

The  interalveolar  connective  tissue  often  contains  groups  of  fat-cells 
(Fig.  164). 

MUCOUS  GLANDS  OF  THE  ORAL  CAVITY. 

The  mucous  glands  are  branched  alveolo-tubular  simple  glands, 
which  produce  a  mucus-  (mucin-)  containing  secretion.  These  pure 
mucous  glands,  in  man,  occur  only  on  the   anterior  surface  of  the   soft 

palate,  on  the  hard  palate,  along  the  edges 
of  the  tongue,  and  in  larger  number  at  the 
root  of  the  tongue,  where  their  excretory 
ducts,  lined  with  (occasionally  ciliated) 
cylinder  epithelium,  not  infrequently  open 
into  the  lingual  tonsils  (Fig.  186).  The 
walls  of  the  tubules  consist  of  a  structure- 
less membrana  propria  and  cylindric  gland- 
cells,  the  appearance  of  which  varies  with 
their  changing  functional  state.  In  the 
empty  state  the  cell  is  smaller,  the  nucleus, 
situated  at  the  base,  is  transverse-oval  (Fig. 
161,  I  b')\  in  the  loaded  state  the  cell  is 
broader  and  the  nucleus  is  pressed  flat 
against  the  wall  (Fig.  161,  I  c,  II).  Usu- 
ally one  and  the  same  mucous  gland,  even 
often  one  and  the  same  tubule,  shows 
gland-cells  in  different  secretory  phases  (Fig.  161,  I),  which  become 
particularly  distinct  upon  the  application  of  fluids  that  stain  mucin.*  The 
pure  mucous  glands  possess  no  secretory  capillaries. 

MIXED    GLANDS    OF    THE    ORAL    CAVITY. 

I.  The  sublingual  gland  (glandula  sublingualis)  is  a  compound 
alveolo-tubular  gland  ;  the  canal  system  consists  of  an  excretory  duct, 
the  branches  of  which  continue  in  very  short  mucous  tubes,  which  pass 


Traces  of  secre- 
tory tubules. 


End-pieces. 


Fig.  165. — Scheme  OF  the  Human  Sub 
LINGUAL  Gland. 


*  Rarely  does  one  find  in  the  human  lingual  mucous  glands  cell-forms  that  correspond 
to  those  represented  in  figure  25  a — c,  page  80. 


THE    DIGESTIVE    ORGANS. 


245 


direct  into  convoluted  end-pieces,  which  are  characterized  by  their  vary- 
ing caUber — often  they  are  evaginated  (Fig.  166).  Intercalated  tubes 
are  wanting  [cf.  p.  87).  The  excretory  duct,  the  sublingual  duct(Bartho- 
lini),  and  Its  coarser  branches  are  composed  of  two-layered  cylinder 
epithelium  and  connective  tissue  with  elastic  fibers.  The  smaller  twigs 
(0.05  mm.  thick  and  more)  possess  only  a  simple  cylinder  epithelium  ; 
they  continue  in  the  secretory  tubes,  w^hose  low  cylinder  cells  show  the 
characteristic  striation  only  in  a  few  places.  The  end-pieces,  enveloped 
in  a  membrana  propria  and  stellate  cells,  are  clothed  with  mucous  and 
serous  cells  ;  the  latter  often  stand  together  in  groups  (Fig.  166),  there- 


A  demilune  consisting  of 
eight  serous  cells. 


Part  of  an  excretory  duct 


•^r^.  Cross-section  v!\\}a. 

(  mucous        cells 

C?^/  and  (left)  thick 

^  ,  i3€/  membrana 

•   ^ii>v_-(  propria. 


Lumina 


Fig.  166. — Thin  Section  of  the  Sublingual  Gland  of  Man.     X  252.     Technic  No.  118. 


fore  the  "demilunes"  are  very  large.  Only  the  serous  gland-cells  are 
furnished  with  free,  branched  intercellular  secretory  capillaries.  The 
connective  tissue  lying  between  the  tubules  and  the  lobules  is  rich  in 
leucocytes. 

2.  The  submaxillar}'  glajid  (glandula  submaxillaris)  is  in  part  pre- 
dominantly an  alveolar  (p.  85),  in  part  an  alveolo-tubular  compound 
gland.  The  canal  system  is  more  differentiated  than  that  of  the  sublin- 
gual gland,  in  so  far  that  distinct  secretory  tubes  and  short  intercalated 
parts  are  present.  The  end-pieces  are  of  two  kinds,  alveolar  and  tubulo- 
alveolar  (Fig.  167).  The  excretory  duct,  the  submaxillary  duct  (Whar- 
toni),  and  its  branches,  respecting   the  epithelium  are  the  same  as  those 


246 


HISTOLOGY. 


;;^  Excretory  duct. 


End- 
pieces. 


Fig.  167. — Scheme  of  the  Human  Submax 

ILLARY  GLA>fD. 


of  the  sublingual  gland,  but  a  richly  cellular  stratum  of  connective  tis- 
sue and  outwardly  to  this  a  thin  layer  of  longitudinally  disposed  muscle- 
fibers  constitute  a  special  peculiarity  of 
the  submaxillary  duct ;  the  •  epithelial 
cells  of  the  secretory  tubes  are  marked 
by  the  characteristic  striation  at  their 
base  and  contain  a  yellow  pigment.  The 
intercalated  pieces  are  clothed  with  cu- 
bical cells  and  lead  into  the  end-pieces, 
that  either  are  clothed  with  serous  gland- 
cells  only — the  greater  portion  of  the 
submaxillary  gland  consists  of  such  end- 
pieces — or  possess  a  mixed  epithelium. 
Here  the  number  of  serous  cells  is  small, 
the  "  demilunes  "  are  formed  of  only  one 
or  a  few  serous  cells  and  therefore  are 
smaller  than  in  the  sublingual  gland. 
Intercellular  secretory  capillaries  of  the 
character  of  those  of  the  parotid  gland 
occur  everywhere  in  the  pure  serous  end-pieces  ;  in  the  mixed  end-pieces 
secretory  capillaries  occur  only  in  connection  with  the  serous  demilune 
cells  ;  they  run  intercellular  up  to  the  demilunes,  in  the  vicinity  of  which 
they  terminate  in  free  branches,  without  reaching  to  the  membrana  pro- 
pria (Fig.  169). 

3.  The  branched  alveolo-tubular  labial  glands  show  the  same  struc- 
ture as  the  submaxillary  gland  ;  the  anterior  lingual  gland  (Nuhn)  and 
the  buccal  glands  also  are  furnished  with  demilunes. 

Not  infrequently  gland  lobules  in  process  of  atrophic  destruction 
are  found  in  the  glands  of  the  oral  cavity  ;  their  end-pieces,  characterized 
by  a  wide  lumen  and  low  gland-cells,  are  surrounded  by  abundant  con- 
nective tissue,  occasionally  also  by  many  leucocytes. 

The  foregoing  description  applies  only  to  the  oral  glands  of  men.  In 
the  lower  mammals  very  far-reaching  differences  often  exist.  The  parotid 
glands  of  the  rabbit,  dog,  and  cat,  also  the  submaxillary  gland  of  the  rabbit, 
agree  in  structure  with  the  parotid  gland  of  man.  The  sublingual  and  submax- 
illary glands  of  the  dog  and  cat  and  the  sublingual  gland  of  the  rabbit  resem- 
ble the  human  sublingual  and  submaxillary  glands. 

The  blood-vessels  ot  the  glands  of  the  oral  cavity  are  very  conspicu- 
ously developed.  The  arterial  stems  as  a  rule  run  alongside  the  main 
excretory  duct,  where  they  divide  into  numerous  branches  which  pass 
between  the  gland  lobules  and  finally  penetrate  within   the  latter,  break 


THE    DIGESTIVE    ORGANS. 


247 


up  into  capillaries  and  form  close  networks  around  the  end-pieces.  The 
capillaries  lie  in  immediate  proximity  to  the  gland-cells  and  are  separated 
from  them  only  by  the  membrana  propria  (see  also  p.  86).  The  larger 
veins  follow  the  course  of  the  arteries. 


'(    ©> 


h^ — fr    ^t 


Serous  gland  cells 


Intercalated  piece. 


■  *^ 

J  r 


Lumen  «»®|      \^ 

Demilune.  Secretory  tube. 

Fig.  168.— Section  of  the  Submaxillary  Gland  of  Adult  Man.     X  252.    Technic  No.  118. 


The  lyniph-vcsscl  tmnklets  run  with  the  coarser  ramifications  of  the 
excretory   ducts,    without  penetrating    into    the    gland   lobules.      Clefts 
between    the    lobules    and    the    end-pieces 
have   been    described   as   lymph   channels. 

The  glands  of  the  oral  cavity  are  pro- 
fusely supplied  with  plexuses  of  medullated 
and  chiefly  nonmedullated  nerves,  along 
the  course  of  which  microscopic  groups 
of  sympathetic  ganglion  cells  occur  (par- 
ticularly in  the  walls  of  the  excretory  ducts). 
The  fine  nonmedullated  nerve-fibers  partly 
ramify  in  the  walls  of  the  blood-vessels, 
partly  form  an  "  epilemmal  "  plexus,  lying 
immediately  upon  the  membrana  propria 
of  the  gland  tubules  ;  trom  this  delicate  filaments  arise,  which  pierce  the 
membrana  propria  and  as  "  hypolemmal  "  fibers  terminate  in  short, 
varicose,  simple  or  branched  ends,  which  lie  against  the  gland-cells. 


J Axial  lumen . 


Intercellular 
secretory 
capillary. 


Demilune. 

Fig.  i6g. — From  a  Section  of  the  Sub- 
maxillary Gland  of  a  Dog.  X  320. 
Technic  No.  126. 


248 


HISTOLOGY. 


The  Teeth. 
The  teeth  of  man  and  the  higher  animals  are  solid  structures, 
which  enclose  in  their  interior  a  cavity,  th.Q  ptdp  cavity,  filled  with  a  soft 
mass,  the  tooth  pulp.  The  portion  of  the  tooth  within  the  alveolus 
or  socket  is  called  the  root  or  fang,  the  free,  exposed  portion,  the 
crozvn  ;  the  juncture  of  these  portions  forms  the  neck,  which  also  is  cov- 
ered by  the  gums.      The  solid  structiL'res  of  the    tooth   consist  of  three 


Enamel. 


Dentine. 


Pulp  cavity. 


Cement.    


\  Crown. 


—  Neck. 


Fig.  170. — Longitudinal  Ground  Section  of  a  Human  Incisor  Tooth.     X  4.     Technic  No.  08. 


different  parts,  (i)  the  dentine,  (2)  the  enamel  with  the  enamel  cuticle 
(cuticula  denti.s),  and  (3)  the  cement.  The  arrangement  of  these  parts  is 
as  follows  :  the  dentine,  which  contributes  the  chief  bulk  of  the  tooth 
and  determines  its  form,  encloses  the  pulp  cavity,  except  on  the  fang 
where  a  narrow  nutrient  canal  admits  the  nerves  and  the  blood-vessels 
to  the  pulp  ;  on  the  crown  the  dentine  is  covered  by  the  enamel,  on  the 
fang  by  the  cement,  so  that  its  surface  is  nowhere  exposed  (Fig.  i/o). 


THE    DIGESTIVE    ORGANS. 


249 


The  dentine  (substantia  eburnea)  is  a  white,  opaque  mass,  harder 
than  bone.  It  consists  of  an  apparently  homogeneous  calcified  ground 
substance,  that  in  reahty  contains  very  delicate,  glutin -yielding  fibrils, 
having  in  general  a  longitudinal  .direction,  and  is  pierced  by  numerous 
minute  canals,  the  dental  canalicicli  {¥\g.  171).  The  latter  begin  with  a 
diameter  of  from  2  to  4  //  at  the  inner  surface  of  the  dentine,  describe  an 
S-shaped  curve,  and  then,  steadily  decreasing  in  caliber,  proceed  in  a 
slightly  wavy  course  in  a  radial  direction  toward  the  outer  surface  of  the 
dentine  ;  there  they  either  terminate  at  the  juncture  of  the  dentine  and 
enamel  in  tapering  ends  or  they  form  a  loop  and  turn  into  a  neighboring 
canaliculus.  During  their  entire  course  they  send  off  numerous  lateral 
branches,  which  establish    communication   with    neighboring   canaliculi. 


Enamel  prisms. 


Dentine. 


Enamel. 


Fig.  171. — From  A  Loxgitudinal  Section  of  the  Lateral 
Part  of  the  Crown  of  a  Hciian  Molar  Tooth.  X 
240.  I,  Dental  canaliculi,  some  extending  into  the 
enamel;  2,  dental  globules  projecting  toward,  3,  the  in- 
terglobular spaces.     Technic  No.  98. 


Cement. 


Fig.  172. — From  A  Longitudinal  Section  of 
THE  Root  of  a  Human  Molar  Tooth. 
X  240.  I,  Dental  canaliculi  interrupted 
by  a  granule  stratum,  with  many,  2,  small 
interglobular  spaces;  3,  bone  lacunje  with 
many   canaliculi.     Technic  No.  98. 


The  matrix  immediately  surrounding  the  dental  canaliculi  is  especially 
dense  and  forms  the  so-called  dental  she atlis.  The  lumen  of  the  denial 
canaliculi  is  occupied  by  the  soft  dental  fibers  (see  tooth  pulp).  In  the 
peripheral  parts  of  the  dentine  lie  the  interglobular  spaces  {¥\g.  17 1), 
uncalcified  portions  of  dentine  varying  greatly  in  size,  toward  which  the 
calcified  dentine  juts  in  the  form  of  usually  hemispherical  protuberances, 
the  dental  globules.  At  the  neck  and  in  the  fang  the  interglobular  spaces 
are  very  numerous  and  very  small  and  form  the  so-called  granule  stratum 
lying  immediately  beneath  the  cement  (Fig.  172).  •    • 

The  enamel  (substantia  adamantina)  is  still  harder  than  the  dentine. 
It  is  exclusively  composed  of  long,  hexagonal,  homogeneous  fibers,* 
from  3  to  6  //  in   thickness,   the   enamel  prisms   (Fig.  173),  which   are 


The  transverse  bands  do  not  appear  until  after  treatment  with  reagents. 


250 


HISTOLOGY. 


firmly  united  with  one  another  by  a  scanty  amount  of  irriguous  cement- 
substance.  They  extend  radially,  with  many  undulations,  from  the  sur- 
face of  the  dentine  to  the  free  surface  of  the  enamel ;  this  is  covered  by 
a  very  thin  but  very  resistant  membrane,  the  dental  cuticle  (cuticula 
dentis). 

The  cement  (substantia  ossea)  coincides  in  its  structure  with  that  ol 
bone.  It  contains  many  Sharpey's  fibers.  Haversian  canals  are  found 
only  in  the  cement  of  aged  individuals  ;  stratification  in  lamellae  is 
seldom  well  defined.      Bone  lacunae  are   absent  near  the  neck. 

The  space  between  the  root  and  the  alveolus  is  occupied  by  the 
richly  innervated  periosteum  of  the  alveolus,  the  "  root  membrane," 
which  is  firmly  united  to  the  cement  by  Sharpey's  fibers,  which  pene- 
trate from  the  inferior  maxilla  through  the  periosteum  into  the  cement. 


Enamel  prisms,     Enamel  prisms  in  trans- 
isolated,  verse  section. 


Fig.  173. 


Fig.  174. 


From  the  Tooth  of  an  Infant. 
nic  No.  100. 


Tech- 


FiG.  175. — Six  Odontoblasts  with  Dental  Fibers,  f; 
p,  pulp  processes.  From  the  pulp  of  an  infant  boy. 
X  240.    Technic  No.  99. 


The  uppermost  portion  of  the  alveolar  periosteum  is   called  the  circular 
dental  ligament  (ligamentum  circulare  dentis). 

The  dental  pulp  is  formed  of  a  soft  connective  tissue,  containing 
delicate  fibers  not  united  in  bundles,  the  cellular  elements  of  which, 
partly  spherical,  partly  stellate  cells,  on  the  surface  are  developed  into  a 
layer  of  slender  cells,  the  odontoblasts  ;  these  send  out  short  processes 
the  pulp  processes  (Fig.  175),  that  are  connected  with  other  elements 
in  the  pulp,  and  long  processes  that  extend  into  the  dental  canaliculi, 
the  previously  mentioned  dental  fibers  (Fig.  175,/).  Elastic  fibers  are 
wanting  in  the  pulp,  as  well  as  in  the  root-membrane.  Vessels  and 
nerves  are  limited  to  the  pulp  of  the  tooth  ;  the  recently  revived  state- 
ment that  the  nerve-fibers  enter  the  dental  canaliculi  stands  greatly  in 
need  of  verification. 


THE    DIGESTIVE    ORGANS. 


251 


DEVELOPMENT  OF  THE  TEETH. 

The  development  of  the  teeth  in  man  begins  early,  already  toward 
the  close  of  the  second  month  of  fetal  life  *  and   is  first  indicated  by  a 


Epithelium  of  the  margin 

of  the  jaw.  Dental  bulbs.         Dental  furrow. 


Dental  ridge.  'S'"' 

A  Papillae. 


Enamel  organs 


Neck  of  bulbs. 


Fig.  176. — Schematic  Representation  of  the  Initial  Processes  in  the  Development  of  the  Teeth,  showing 
the  formation  of  three  teeth.  The  anlage  of  each  anterior  tooth  is  seen  in  section;  the  cut  surface  of  the 
papilla  is  stippled,    k.  Free  edge  of  the  dental  ridge. 

proliferation  of  the   epithelium  of  the  margin  of  the  jaw,   which  in  the 
form  of  a  continuous  ridge  grows  obliquely  into  the  subjacent  connective 


Cartilaginous- 
nasal  septum. 


Nasal  cavity. 


Anlage  of  the 
osseous 
upper  jaw. 


Oral  canty. 


Tongue. 


*-^  ^  ■*  ^       osseous 

lower  jaw. 

Fig.  177. — Frontal  Section  of  the  Head  of  an  Embryo  Sheep,  4  cm.  long.     X  15.    Technic  No.  loi. 


tissue.      This  ridge,  the  dental  ridge  ("enamel    germ"  )  (Fig.   176,  a), 
develops    on    its    lateral    (labial)   surface    knob-like    protuberances,   the 

*That  which  at  an  earlier  period  (the  fortieth  day)  has   been  described  as  the  anlage  of 
the  tooth,  is  not  this  alone,  but  includes  the  anlage  of  the  labial  furrow. 


2^2 


HISTOLOGY. 


_,,---'Epithelium\ 


^''Tunica 

propriai 


of  the  oral  mu 
'  cous  mem- 
,      brane 


f% 


.  ^'-'-jl^^i' '-'  "Papilla. 


"Enamel  organ 


Lower  lip. 


Orbicularis  oris  muscle  in 
transverse  section. 


"""Osseous    trabeculae  of  the 
lower  jaw. 


Fig.   178. — Cross-section  of  the  Lower  Jaw  of  a  Human  Embryo  Four  Months  Old.     X  42. 

Technic  No.  loi. 


Thickened 
epithelium 
of  the  oral 
mucous 
membrane. 


=v5^giS% 


■^"'"j, " 


Outer  enamel  cells 

Enamel  pulp 
Inner  enamel  cells 


Neck  of  the  bulb 


Free  edge  of  the 
dental  ridge- 


Papilla. 


Fig.    179. — From  a  Cross-section  of  the  Upper  Jaw  of  a  Human  Embryo  Five  Months  Old.     X  42- 

Technic  Xo.  loi 


THE    DIGESTIVE    ORGANS. 


253 


dental  bulbs  (b),  corresponding  in  number  to  the  temporary  teeth,  while 
coincidently  in  the  tunica  propria  as  many  aggregations  of  closely  packed 
connective-tissue  cells  arise,  the  young  dental  papilla  (b)  (tenth  week). 
The  latter  advance  obliquely  from  the  external  or  labial  side  out  of  the 
depths  to  the  inner  or  lingual  side  toward  the  surface  and  are  embraced 
by  the  dental  bulbs  in  such  a  manner  that  these  form  an  epithelial  hood 
for  the  dental  papillae.  In  this  way  each  bulb  becomes  an  enamel  orgati. 
Meanwhile  the  dental  ridge  has  taken  a  more  nearly  vertical  position  (c). 


zjfe*''-: 


^  53^'*^ 


•M 


■'o'i' 


i>'  6^ 


Cross-section  of 
the  orbicularis 
oris  muscle. 


Labial  gland. 


)ental  ridge. 

V- 

Enamel 
organ. 

Sij<^-^ 


Enamel. 

Dentine. 
Pulp. 

Bone. 


Fig.  180. — Vertical  Section  through  the  Lip  and  Jaw  of  a  Human  Fetus  of  Six  and  a  Half  Months. 

X  9.    Technic  No.  10 1. 


At  about  this  time,  too,  a  longitudinal  groove  on  the  margin  of  the  jaw 
is  visible,  the  dental /urrozv,  which  exteriorly  marks  the  place  from  which 
the  dental  ridge  grew  into  the  depths.  The  time  of  the  appearance  of 
the  dental  furrow  varies  ;  frequently  it  is  present  in  the  initial  stages.  It 
disappears  later.  The  original  broad  attachment  between  the  dental 
ridge  and  the  enamel  organ  becomes  diminished  by  partial  constriction 
(indicated  in  the  scheme  c  by  a  stippled  line)  and  finally  is  reduced  to  a 
slender  cord,  the  nec/c  of  the  bulb.  Meanwhile  the  papilla  and  the 
enamel  organ  grow  further  into  the  depths,  so  that  the  free  edge  of  the 


254 


HISTOLOGY. 


dental  ridge    does   not   extend   even   to   half  the   depth   of    the   enamel 
organ  (Fig.  176  and  Fig.   179). 

At  the  same  time  the  elements  of  the  enamel  organ  undergo  further 
differentiation.      The  inner  cells,  resting  upon  the  papilla,  develop  into 


Dental  sack. 
Outer  layer.        Inner  layer. 


Outer  enamel  cells. 


Enamel  pulp. 


Inner  enamel  cells 
(enamel  membrane). 


Enamel. 


Dentine. 


Odontoblasts 


Dental  papilla  (future  pulp) 


Blood-vessel. 
Bony  trabecula  of  the  lower  jaw 


Fig.  181. — Longitudinal  Section  of  a  Young  Milk-tooth  of  a  Newborn  Dog.     X  42.  Technic  No.  loi . 

tall  cylinders,  called  the  inner  enamel  cells  (Fig.  179);  their  inner  sur- 
face is  provided  with  a  cuticular  border.  The  peripheral  cells,  on  the 
contrary,  steadily  decrease  in  height  (Fig.  182),  until  finally  they  are  re- 
duced to  flattened  elements,  the  onter  enamel  cells  ;  the  cells  lying  between 


THE    DIGESTIVE    ORGANS.  255 

the  inner  and  the  outer  enamel  cells,  by  an  abundant  increase  of  the 
intercellular  substance,  become  transformed  into  stellate,  anastomosing 
elements  and  constitute  the  cnmncl  pulp  (Fig.  182).  At  the  point 
where  the  layer  of  inner  enamel  cells  bends  over  into  the  layer  of 
outer  enamel  cells  the  enamel  organ  grows  further  into  the  depths,  until 
it  has  reached  the  lower  end  of  the  anlage  of  the  tooth.  In  a  measure 
the  enamel  organ  forms  the  mold,  or  the  matrix,  in  which  the  tooth 
develops.  The  determination  of  the  shape  of  the  future  tooth  is  the  first 
function  of  the  enamel  organ  ;  the  second  is  the  production  of  the  enamel. 

Cuticular  border.    Enamel^prisms.     Cement  substance. 

\  \  Calcified,    uncalcified  dentine. 


For 

orientation ! 

This  much  is  sketched  with  the 
higher  magnification. 
Inner 

Fig.  1S2. — Portion  of  a  Longitudinal  Section  of  an  Incisor  Tooth  of  a  Newborn  Kitten.     X  300. 

Technic  Xo.  10 1. 

In  this  section  the  young  enamel  prisms  have  been  pulled  out  of  their  spaces  in  the  cement  substance  and  appear 

as  Tomes's  processes  of  the  inner  enamel  cells. 


Enamel  is  formed  only  by  the  oiamcl  nievtbranc,  that  is,  by  the 
upper  portion  of  the  layer  of  inner  enamel  cells  ("  ameloblasts  "),  envel- 
oping the  crown  of  the  tooth.  Each  cell  of  this  membrane  produces 
a  substance  which  eventually  calcifies  and  becomes  an  enamel  prism, 
that  is  joined  to  its  neighbors  by  an  at  first  very  abundant  cement  sub- 
stance. In  the  further  course  of  development  the  enamel  prisms  increase 
in  thickness  at  the  expense  of  the  cement  substance. 

The  lower  inner  enamel  cells,  surrounding  the  root,  take  no  part  in 


256  HISTOLOGY. 

the  production  of  the  enamel ;  they  decrease  in  height  and,  since  here 
the  enamel  pulp  soon  disappears,  place  themselves  directly  against  the 
outer  enamel  cells.  The  two  layers  here  form  the  epithelial  sheath  of  the 
root  (Fig.  181). 

Before  the  production  of  enamel  has  begun  the  first  dentine  has  been 
formed  (about  the  twentieth  week).  The  superficial  cells  of  the  dental 
papilla  elongate  and  become  the  odontoblasts,  which  produce  the  at  first 
uncalcified  dentine  (Fig.  182).  Development  of  odontoblasts  takes 
place  only  so  far  as  the  epithelial  sheath  reaches.  As  soon  as  the  first 
dentine  is  formed,  the  epithelial  sheath  at  this  point  undergoes  regressive 
change,  through  connective -tissue  ingrowths  from  the  dental  sack  (see 
below),  which  penetrate  between  the  epithelial  cells.  This  regression 
begins  at  the  lower  border  of  the  enamel,  so  that  the  deepest  part  of  the 
epithelial  sheath  loses  its  connection  with  the  enamel  organ.  With  the 
completed  growth  of  the  tooth  the  last  remnant  of  the  epithelial  sheath 
disappears. 

Before  the  production  of  enamel  and  dentine  begins  the  connection 
between  the  dental  ridge  and  the  surface  is  dissolved  *  (Fig.  176  D)  ;  the 
connective  tissue  surrounding  the  entire  anlage  of  the  tooth  arranges  it- 
self in  a  compact  membrane,  the  dental  sack,  in  which  later  on  an  inner 
looser  and  an  outer  denser  stratum  can  be  distinguished  (Fig.  181).  The 
enamel  cuticle  (cuticula  dentis)  and  the  cement  do  not  appear  until  after 
birth,  shortly  before  the  irruption  of  the  tooth.  The  cuticula  is  pro- 
duced by  the  merging  of  the  cuticular  borders  of  the  enamel  cells  into  a 
firm,  homogeneous  membrane  ;  the  cement  is  a  product  of  the  dental 
sack.  At  the  irruption  of  the  tooth  the  enamel  cells  and  the  enamel 
pulp  degenerate,  not  a  trace  remaining. 

Accordingly,  the  completed  tooth  is  in  part  of  epithelial  origin  (the 
enamel),  in  part  derived  from  the  connective-tissue  dental  papilla  (the  den- 
tine), which  may  be  compared  with  a  papilla  of  the  mucous  membrane,  the  re- 
mains of  which  persist  in  the  adult  as  the  dental  pulp.  The  cement  is  in  a 
measure  an  accessory  structure  contributed  by  neighboring  tissues. 

The  permanent  teeth  develop  in  the  same  manner  as  the  temporary 
teeth  ;  in  the  twenty-fourth  week  new  dental  bulbs  arise  on  the  edge  of  the 
dental  ridge  growing  further  into  the  depths,  which  embrace  new  papillae 
penetrating  from  the  side.f  The  anlage  of  the  permanent  tooth  at  first  lies  in 
the  same  alveolus  with  the  anlage  of  the  milk-tooth  and  only  later  is  enclosed 

*  The  dental  ridge  has  previously  become  a  much -perforated  plate,  from  which  on  all  sides 
short,  jagged  excrescences  arise.  Remains  of  the  dental  ridge  may  still  be  found  in  the  gums 
of  newborn  children  and  were  erroneously  regarded  as  glands  (glandulse  tartaricse). 

f  The  anlages  of  the  permanent  molar  teeth  originate  in  a  lengthening  of  the  posterior 
end  of  the  dental  ridge,  which  grows  in  the  depths  of  the  mucous  membrane  backwards  toward 
the  angle  of  the  inferior  maxilla. 


THE    DIGESTIVE    ORGANS. 


257 


in  a  separate  alveolus.  With  the  exchange  of  the  teeth  the  septum  between 
these  alveoli  is  resorbed  ;  the  dentine  and  cement  of  the  root  of  the  milk- 
tooth  likewise  undergo  resorption,  which  is  effected  by  ostoclasts  in  the  same 
manner  as  in  the  bones. 

The  Tongue. 
The  bulk  of  the  tongue  is  formed  of  striated  muscles,  the  separate 
bundles  and  fibers  of  which  freely  interlace,  that  over  the  greater  part  of 
their  circumference  are  covered  by  a  continuation  of  the  oral  mucous 
membrane.  The  muscles  are  arranged  in  three  planes  :  (i)  vertically 
ascending  (in  the  genioglossus,  lingualis,  and  hyoglossus) ;  (2)  trans- 
versely i^w  the  lingualis),  and  {-^  longittidinally  (in  the  lingualis  and  stylo- 
glossus). Since  the  muscle  bundles  cross  one  another  for  the  most  part 
at  right  angles  they  form   a  beautiful   network,  visible  in  sections.     A 


Epithelium. 


Epithelium. 

Tunica 

v„;--av_i, — ■ v,  ;  '-.•••.  '  propria. 

'^1?^/.  "      ■  ■■ 


Tunica 


Fig.  183. — Longitudinal  Section  of  the  Mucous 
Membrane  of  the  Human  Tongue.  X  30. 
1,  Section  of  two  filiform  papillae,  each  of  which 
bears,  2,  three  secondary  papillae  ;  3,  compound,  4, 
simple  process  of  epithelium,  the  surface  of  which 
is  covered  with  masses  of  loosely  attached  squa- 
mous epithelial  cells.     Technic  No.  102. 


Fig.  184. — Longitudinal  Section  of  the  Mucous 
Membrane  OF  the  Human  Tongue.  X  30.  i, 
Fungiform  papilla  with,  2,  secondary  pa pillas  ;  3, 
stalk  of  fungiform  papilla;  4,  small  fiHform 
papilla.     Technic  No.  102. 


median  septum,  the  septum  lingucE,  divides  the  muscle  masses  of  the 
tongue  into  a  right  and  a  left  half.  The  septum  begins  low  at  the  body 
of  the  hyoid  bone,  gradually  increases  in  height,  attains  its  greatest  ele- 
vation in  the  middle  of  the  tongue,  then  gradually  slopes  down  forward 
and  disappears  ;  it  does  not  extend  through  the  entire  thickness  of  the 
tongue,  but  ceases  at  a  distance  of  about  3  mm.  from  the  surface  of  the 
organ.     The  septum  is  composed  of  tough  connective  tissue  fibers. 

The  mucous  membrane  of  the  tongue,  like  that  of  the  oral  cavity, 
consists  of  an  epithelium,  a  tunica  propria,  and  a  submucosa,  but  is 
characterized  by  the  conspicuous  development  and  compHcated  structure 
of  the  papillje.  Three  forms  of  papillje  are  distinguished  :  the  Jilifor7n  or 
conical,  t\\e  fungiform  or  clavate,  and  the  vallate  or  circiimvallate  papillcB. 

The  filiform  papillcs  (papiUx  conicse)  (Fig.  183)  are  cylindrical  or 
17 


2S8 


HISTOLOGY. 


conical  elevations  of  the  tunica  propria,  bearing  on  the  summit  from  five 
to  twenty  small  secondary  papillae  (2).  They  are  composed  of  distinctly 
fibrous  connective  tissue  and  numerous  elastic  fibers  and  are  covered 
with  a  powerful  stratified  squamous  epithelium,  that  over  the  secondary 
papillae  not  infrequently  forms  a  number  of  filamentous,  horny  processes. 
The  filiform  papillae  are  very  numerous  and  are  distributed  over  the 
entire  surface  of  the  tongue  ;  they  vary  in  height  from  0.7  to  3  mm. 

^\ie.  fungiform  papillce  (papillae  clavatae)  (Fig.  184)  are  spherical 
structures  connected  with  the  tunica  propria  by  a  slightly  constricted 
stalk;  their  entire  surface  is  beset  with  secondary  papillae  (2).  They 
consist  of  a  distinct  braidwork  of  connective -tissue  bundles,  that  contain 
but  few  elastic  fibers.     The  epithelial  cover  is  somewhat  thinner  than  on 


Secondary  papillce 


Epithelium 


Tunica  propria 


Submucosa 


Taste-buds 

(indistinct). 


Serous  glands. 


IMuscle-fibers. 


Fig.  185. — Vertical  Section  of  a  Vallate  Papilla  of  Man.     X  30-    Technic  No.  102. 


the  fihform  papillae  and  is  not  cornified.  The  fungiform  papillae,  not  so 
numerous  as  the  filiform,  are  also  distributed  over  the  entire  surface  of 
the  tongue  and  in  the  living  they  are  usually  easily  distinguished  by 
their  red  color,  due  to  the  capillaries  shimmering  through  the  trans- 
parent epithelium.     Their  height  varies  from  o.  5  to  1.5  mm. 

The  vallate  papill(E  (papillae  circumvallate)  (Fig.  185)  are  often  very 
irregularly  developed  ;  they  resemble  broad,  flattened,  fungiform  papillae 
and  are  separated  from  the  remaining  mucous  membrane  by  a  circular 
furrow  varying  in  depth  ;  the  mucous  membrane  of  the  opposite  side  of 
the  furrow  is  designated  the  zvall.  These  papillae  are  composed  of  con- 
nective tissue  like  that  of  the  fungiform  papillae,  but  in  man  not  infre- 
quently contain  longitudinally  or  obliquely  disposed  smooth  muscle- 
fibers  ;    they  are  also  found  in  the  wall,   where  their  arrangement  is 


THE    DIGESTIVE    ORGANS. 


259 


circular.  The  vallate  papilla;  *  possess  secondary  papillae  only  on  the 
upper,  not  on  the  lateral  surface.  In  the  epithehum  covering  their  sides, 
occasionally  also  in  that  on  the  wall,  lie  the  end  apparatus  of  the  gusta- 
tory nerves,  the  taste-buds  (see  The  Gustatory  Organ) ;  in  the  wall  soli- 
tary nodules  of  adenoid  tissue  are  occasionally  found  {cf.  p.  146).  The 
vallate  papillae  are  few  in  number,  from  8  to  15,  and  only  occur  at  the 
posterior  end  of  the  upper  surface  of  the  tongue.  They  are  from  i  to 
1.5  mm.  high  arid  from  i  to  3  mm.  broad.  On  each  posterior  lateral 
margin  of  the  tongue  is  a  group  of  parallel  folds  of  the  mucous  mem- 
brane, named  \ht  foliate  papilla,  that  are  distinguished  by  their  wealth  of 
taste-buds.    The  foliate  papillae  are  especially  well  developed  in  the  rabbit. 


n n  «>.-'N 


//- 


-  Epithelium. 


A 


Ah 


//- 


Tunica  propria. 


Fig.  186. — Vertical  Section  of  a  Lingual  Tonsil  of  Adult  Man.  X  20.  1.  Crypt  of  the  tonsil,  containing 
migrated  leucocytes.  2.  Epithelium  of  the  crypt,  infiltrated  with  leucocytes  on  the  left  and  at  the  base, 
almost  intact  on  the  right.  3.  Xodules  of  adenoid  tissue  containing  germinal  centers:  Z',  nodule  cut  through 
the  middle,  /-,  through  the  side,  P.  at  the  periphery.  4.  Fiber  capsule.  5.  Section  of  the  excretory  duct 
of  a  mucous  gland.     6.  Blood-vessel.     Technic  Xo.  102. 

The  siibnuicosa  at  the  tip  and  on  the  back  of  the  tongue  is  firm  and 
resistant  (fascia  linguae),  and  intimately  connected  with  the  underlying- 
parts. 

The  lingual  to?tsils  (folliculi  linguales). — The  mucous  membrane  of 
the  root  of  the  tongue  extending  from  the  vallate  papillae  to  the  epiglottis 
is  peculiarly  modified  by  the  development  of  the  lingual  tonsils.  They 
are  spherical  aggregations  of  adenoid  tissue,  from  i  to  4  mm.  in  size, 
that,  situated  in  the  uppermost  stratum  of  the  tunica  propria,  form  easily 


*Not  infrequently  widely  branched  epithelial  proliferations,  in  the  form  of  deep-reach- 
ing pegs,  occur  in  the  vallate  papillae,  that  may  separate  by  constriction  from  the  surface  epithe- 
lium and  then  represent  concentrically  stratified  bodies,  the  "epithelial  pearls." 


26o 


HISTOLOGY. 


perceptible  macroscopic  elevations.  In  the  middle  of  the  same  a  punctate 
opening  *  may  be  seen,  the  entrance  to  the  narrow,  deep  crypt,  which  is 
clothed  by  a  continuation  of  the  stratified  epithelium  of  the  oral  mucous 
membrane.  Encircling  this  epithelium  lies  adenoid  tissue,  which  contains 
a  variable  large  number  of  lymph  nodules  with  germinal  centers  (p.  145) 

Emigrating  leucocytes.        Fragments  of  epithelium. 


Emigrated  leuco g> 

cytes.  fi, 


[Epithelium. 


Adenoid  tissue  of 

the    tunica 

propria. 


•}      ' 


J?iwv.,, 


F-<> 


Fio.  187. — From  a  Thin  Section  of  a  Lingual  Tonsil  of  Man.  X  420.  On  the  left  the  epithehum  is  free 
from  leucocytes,  on  the  right  many  leucocytes  are  wandering  through.  The  epithelium  is  torn  and  smaller 
or  larger  fragments  of  it  are  seen  lying  between  the  broad  passages  made  by  the  leucocytes.  Technic  No. 
102. 


and  is  sharply  separated  from  the  fibrillar  connective  tissue  of  the  tunica 
propria  ;  when  the  tonsils  are  well  developed  the  connective  tissue  is 
arranged  in  circular  strands  about  the  adenoid  tissue  and  so  forms  the 
/ider  capsule  (Fig.  i86,  4).  Under  normal  conditions  numerous  leuco- 
cytes of  the  adenoid  tissue  continually  wander  through  the  epithelium 


*  This  was  formerly  regarded  as  the  excretory  duct  of  the  lingual  tonsil,   which  was 
regarded  as  a  gland. 


THE    DIGESTIVE    ORGANS.  261 

into  the  crypt  "^  and  from  there  into  the  mouth  cavity  ;  they  are  readily 
found  in  the  saliva,  as  " mucous "  and  "salivary  "  corpuscles.  The  cpitJic- 
liiun  is  often  much  torn  fin  consequence  (Fig.  187),  or  is  infiltrated  with 
leucocytes  to  such  a  degree  that  its  boundary  toward  the  tunica  propria 
cannot  be  definitely  determined. 

Three  kinds  of  branched  glands  occur  in  the  lingual  mucous 
membrane  and  in  the  superficial  strata  of  the  lingual  musculature.  The 
jTt'rf^/^j- glands  occur  only  in  the  vicinity  of  the  vallate  and  foliate  papillse, 
the  vmcoiis  glands  in  the  root  and  along  the  edges  of  the  tongue,  the 
mixed  diniQnor  lingual  gland  (Nuhn)  in  the  tip  of  the  tongue.  (Regard- 
ing the  minute  structure  of  these  glands,  see  the  chapter  on  The  Glands 
of  the  Oral  Cavity.) 

The  blood-vessels  of  the  lingual  mucous  membrane  form  networks 
spread  out  parallel  to  the  surface,  from  which  twigs  ascend  to  all  the 
papillae  up  into  the  secondary  papillae.  At  the  root  of  the  tongue  small 
arteries  pierce  the  fiber  capsule  of  the  lingual  tonsils  and  break  up 
into  capillaries  that  penetrate  to  the  interior  of  the  nodules.  The  blood- 
vessels of  the  glands  form  capillary  networks  around  the  end-pieces. 

The  lymph-vessels  of  the  tongue  are  arranged  in  two  nets  ;  a  deep 
net  consisting  of  larger  vessels,  and  a  superficial  net,  which  takes  up  the 
lymph-vessels  of  the  papillae.  The  lymph-vessels  at  the  root  of  the 
tongue  are  very  richly  developed  ;  they  form  networks  encircling  the 
nodules  of  the  lingual  tonsils. 

The  nerves  of  the  lingual  mucous  membrane,  the  glossopharyngeal 
and  the  lingual,  contain  ganglion  cells,  that  occur  scattered  in  the  vallate 
papillae  and  the  wall  and  in  groups — the  so-called  Remak's  hemiganglia 
— beneath  nearly  every  one  of  the  walled  papillae  ;  the  nerve  endings 
behave  partly  as  those  of  other  portions  of  the  oral  mucous  membrane, 
partly  they  enter  into  intimate  relation  with  the  taste-buds  [cf.  The 
Gustatory  Organ). 

THE  SOFT  PALATE  AND  THE  PHARYNX. 

The  soft  palate  on  its  anterior  surface  is  covered  with  a  stratified 
squamous  epithelium  ;  the  tunica  propria  is  furnished  with  tall  papillae 
and  separated  by  a  continuous  layer  of  thick  elastic  fibers  from  the  sub- 
mucosa.  In  the  latter  are  found  adipose  tissue,  cross-striped  muscles, 
and  a  powerful,  well-guarded  stratum  of  mucous  glands,  the  bodies  of 
which  often  extend  far  into  the  muscles,  while  their  long  excretory  ducts 

*  Regarding  the  role  of  the  migrating  leucocytes  see  p.  137,  remark  *. 

fThe  gaps  arising  in  this  way  close  so  soon  as  the  leucoc)'tes  have  wandered  through. 


262  HISTOLOGY. 

are  directed  obliquely  downward.  The  minuter  structure  agrees  with 
that  of  the  lingual  mucous  membrane.  The  posterior  surface  of  the  soft 
palate,  upward  for  a  distance  from  the  free  border,  is  clothed  with  a 
mucous  membrane  containing  no  adipose  tissue,  but  otherwise  of  the 
same  structure  ;  at  a  level  varying  individually  this  changes  into  typical 
respiratory  nasal  mucous  membrane  with  mixed  glands  (see  The  Olfac- 
tory Organ) ,  the  latter  occasionally  may  be  traced  to  the  uvula. 

The  wall  of  the  pharynx  consists  of  three  membranes  :  a  mucous, 
a  muscular,  and  a  fibrous  membrane.  The  mucous  membrane,  consist- 
ing of  stratified  squamous  epithelium  and  a  tunica  propria  with  papillse, 
is  sharply  separated  from  the  muscular  membrane  by  a  robust  layer  of 
longitudinally  disposed  elastic  fibers;  this  "elastic  border-stratum" 
sends  processes  into  the  muscular  membrane  that  embrace  the  individual 
muscle-fibers  and  gradually  disappears  downward,  toward  the  beginning 
of  the  esophagus  ;  upward,  too,  the  border-stratum  diminishes  in  thick- 
ness, but  where  the  musculature  is  wanting  it  forms  a  dividing  layer 
between  the  tunica  propria  and  the  submucosa  *  of  the  connective-tissue 
mucous  membrane.  Numerous  alveolo-tubular  branched  simple  glands, 
mucous  glands  of  the  structure  of  the  lingual  mucous  glands,  lie  beneath 
the  elastic  border-stratum  ;  their  excretory  ducts  are  often  surrounded 
by  aggregations  of  leucocytes.  In  the  pharynx  also  atrophic  mucous 
glands  occur.  In  the  upper  division  of  the  pharynx  (pars  nasalis) 
the  epithelium  changes  into  the  many-row,  ciliated  cylinder  variety, 
the  lower  limit  of  which  is  subject  to  considerable  variation  ;  the  glands 
occurring  here  lie  above  the  border-stratum  and  agree  in  structure  with 
the  mixed  glands  of  the  respiratory  nasal  mucous  membrane. 

Very  richly  developed  is  the  adenoid  tissue.  Between  the  pillars  of 
the  fauces  it  forms  conspicuous  aggregations,  one  on  each  side,  known  as 
the  palatine  tonsils  {tonsilla  palatind),  which  in  respect  to  their  structure 
in  man  and  in  many  animals  correspond  to  a  number  of  large  lingual 
tonsils  (p.  259).  The  leucocytes  that  wander  through  the  epithehum 
of  the  tonsils  into  the  crypts  are  so  numerous  that  they  may  be  regarded 
as  the  most  fertile  source  of  the  salivary  corpuscles.  Many  mucous 
glands  lie  in  the  neighborhood  of  the  tonsils.  The  adenoid  tissue  is 
also  vigorously  developed  in  the  nasal  portion  of  the  pharynx,  where  it 
forms  a  conspicuous  mass,  the  "pharyngeal  tonsil,"  which  agrees  in 
structure  wdth  the  palatine  tonsils,  excepting  that  the  adenoid  tissue  is  less 
sharply  circumscribed.      Here,  too,  many  leucocytes  migrate  through  the 


*  Passing  upward  the  submucosa  becomes  greatly  strengthened  and  as  the  pharyngo-basilar 
fascia  is  attached  to  the  base  of  the  cranium. 


THE    DIGESTIVE    ORGANS. 


263 


epithelium.     The  development  of  all  the  adenoid  tissue  of  the  oral  cavity 
and  of  the  pharynx  is  subject  to  considerable  variation. 

The  vuiscidar  iiicinbranc  (the  constrictor  muscles  of  the  pharynx) 
consists  of  striated  muscle-fibers,  the  description  of  which  belongs  to  the 
domain  of  macroscopic  anatomy.  The  fibrous  Jiteinbranc  is  a  dense- 
fibered  connective  tissue,  richly  interlaced  with  elastic  fibers.  Blood- 
vessels, lymph-vessels,  and  nerves  are  distributed  in  the  same  manner  as 
in  the  oral  cavity. 


Squamous  epithe- 
lium. 

Tunica  propria. 
/•  Muscularis 

./      mucosae. 
Y   .     _Submucosa./ 


Mucous 
mem- 
brane. 


\     Circular  muscles.    Imuscu- 
-r  .^^_„^^^^ _     -     mr  Longitudmal  mus-  >   laris 

Cluster  of  fat-cells  

Mucous  gland 
Lymph  nodule. 
Fig.  188. — Transverse  Section  of  the  Upper  Third  of  the  Human  Esophagus.     X  s-    Technic  No.  104, 


B.    RUMPGUT. 

the  foregut. 

The  Esophagus. 

The  wall  of  the  esophagus  comprises  a  mucous,  a  muscular,  and  a 
fibrous  membrane.  The  ))uicoiis  membrane  is  composed  of  a  stratified 
squamous  epithelium  (Fig.  189),  of  a  tunica  propria  beset  with  papillae, 
following  this  of  a  stratum  of  longitudinally  disposed  smooth  muscle- 
fibers,  the  miisciilaris  mncostc ;  beneath  *  this  is  the  siibmucosa,  which 
consists  of  loose  bundles  of  connective  tissue  and  contains  small 
mucous  glands  of  the  structure  of  the  lingual  mucous  glands.  Their  ex- 
cretory duct,  usually  running   obliquely  cardia-ward,  before  its  passage 


264  HISTOLOGY. 

through  the  muscularis  mucosse  often  is  widened  ampulla-wise  ;  attached 
to  it  within  the  territory  of  the  tunica  propria  is  a  lymph  nodule.  The 
number  of  these  glands  fluctuates  greatly  individually  ;  as  a  rule  they 
are  more  numerous  in  the  upper  half  of  the  esophagus.  Not  seldom 
these  glands,  too,  exhibit  phenomena  of  degeneration  (p.  246). 

In  addition  to  these  glands  of  the  submucosa  the  tunica  propria  of  the 
extreme  lower  end  of  the  esophagus,  in  a  zone  from  one  to  four  millimeters 
broad,  contains  branched  tubular  simple  glands,  with  the  excretory  ducts  often 
widened  ampulla-shape,  which,  in  contradistinction  to  those  of  the  submucous 
glands,  always  enter  the  epithelium  at  the  apex  of  a  papilla.  In  their  micro- 
scopic structure  these  "cardiac  glands"  resemble  true  gastric  glands  and  are 
distinguished  from  them  by  their  profuse  branching,  as  well  as  by  the  indi- 
vidual variation  in  the  presence  or  absence    of  the  parietal  cells.      Groups  of 


Mucosa. 


Muscularis. 


Fibrosa. 


Fig.  189. — From  a  Cross-section  of  the  Middle  Third  of  the  Human  Esophagus.  X  io.  i.  Stratified 
squamous  epithelium.  2.  Tunica  propria.  3.  Muscularis  mucosae.  4.  Submucosa.  5.  Circular  muscles. 
6.  Longitudinal  muscles,     g.  Blood-vessel.     Technic  No.  104- 

just  such  glands  lie  laterally  in  the  initial  portion  of  the  esophagus  at  the  level 
between  the  cricoid  cartilage  and  the  fifth  tracheal  ring,  occasionally  also 
farther  below  ;  their  number,  like  that  of  the  cardiac  glands,  is  subject  to 
great  individual  variation.* 

The  muscular  Tnembrane  in  the  cervical  portion  of  the  esophagus 
consists  of  striated  muscle-fibers,  which  in  the  lower  portion  are  re- 
placed by  smooth  muscle-fibers.  The  latter  are  arranged  in  two  strata, 
an  inner  circular,  in  which  the  direction  of  the  muscle-fibers  is  not 
everywhere  exactly  transverse,  and  an  outer,  not  continuous  longitudinal 
layer.  The  fibrous  nicvibranc  consists  of  compact  connective-tissue 
interspersed  with  numerous  elastic  fibers.      The  distribution  of  the  blood- 

*  Examined  with  the  unaided  eye  such  groups  have  the  appearance  of  erosions,  because 
at  these  places  the  surface  epithelium  is  not  stratified  squamous  but  gastric  epithelium  (page 
265).  The  delicate  epithelium  possibly  is  the  cause  of  the  predisposition  of  this  locality  to 
pulsation  diverticula  ;  the  ampullae  favor  the  tendency  to  the  development  of  cysts. 


THE    DIGESTIVE    ORGANS. 


vessels,  lymph-vessels  and  nerves  is  the  same  as  in  the  pharynx.  Be- 
tween the  circular  and  longitudinal  layers  of  the  muscularis  the  nerves 
form  a  net-like  plexus,  containing  small  groups  of  ganglion  cells  (see 
plexus  myentericus,  p.  281). 

The   Stomach. 

The  wall  of  the  stomach  is  from  2  to  3  mm.  thick  and  comprises 
three  membranes  :  a  mucous,  a  muscular,  and  a  serous  membrane. 

The  vuicous  membrane,  sharply  marked  off  from  the  white  esopha- 
geal mucous  membrane 


Epithelium 


j[/^^,^.,^rfr^^^^ 


Tunica  propria 


Mucosa. 


Muscularis. 


by  its  reddish-gray  color, 
consists  of  an  epithelium, 
a  tunica  propria,  a  mus- 
cularis mucosse,  and  a 
submucosa  (Fig.  190). 

The  epithelium  is  a 
simple  cylinder  epithe- 
lium, the  elements  of 
which  produce  mucus. 
Two  divisions  can  usu- 
ally be  distinguished  in 
them ;  an  upper  chiefly 
mucous  (Fig.  25  <:,p.  80), 
enclosing  the  centro- 
some,  and  a  lower  proto- 
plasmic division  (Fig. 
25  />),  which  latter  con- 
tains the  oval,  round, 
or  flattened  nucleus. 
The  dimensions  of  the 
mucous  division  (the  secretion  collecting  center)  vary  greatly,  according 
to  the  functional  state  of  the  cell  {cf.  Fig.  25).  The  gastric  epithelial  cells 
often  closely  resemble  goblet  cells  (p.  273). 

The  hinica  propria  is  composed  of  a  mixture  of  fibrillar  and  reticular 
connective  tissue,  of  elastic  fibers,  and  of  an  extremely  variable  number 
of  leucocytes,  that  occasionally  lie  closely  aggregated  and  form  solitary 
lymph  nodules.  The  tunica  propria  contains  so  many  glands  that  its 
tissue  is  limited  to  delicate  septa  between  and  a  thin  stratum  below  the 
tubules.  In  the  pyloric  division  the  glands  are  farther  apart ;  there  the 
tunica  propria  is  conspicuously  developed  and  not  infrequently  is  elevated 
in  filamentous  or  leaf-like  villi. 


(Inner  circular  layer 
of  muscle. 


I  Outer  longitudinal 
layer  of  muscle. 


Serosa. 


Fig.  190. — Transverse  Section  of  the  Wall  of  a  Him  .  ~.  :  h. 
X  15.  The  tunica  propria  contains  glands  standing  so  close  to- 
gether that  its  tissue  is  visible  only  at  the  base  of  the  glands  toward 
the  muscularis  mucosa.     Technic  Xo.  105. 


266  HISTOLOGY. 

The  zlands  of  the  stomach  are  of  two  kinds  :  the  one  kind  is  situ- 


Epithelium  of  the  surface. 


j_^^'  )  Gastric  pit. 


Neck 


Chief  cells.  ^ ^^  '°i 


Leucocytes. 


Smooth  muscle-fibers. 


a  \'wp'  ¥' 


?3 


I    1,9    0 1    t, 


f     ^ 


Body 


'  of  the  gland. 


\0  c  \ 


_Ji 


Fundus" 


Parietal  cell. 


,         ^^  .        <^o■ 

Fig.  ipi. — Vertical  Section  of  the  Mucous  Membrane  of  a  Human  Stomach,  in  the  Vicinity  of  the 

Fundus.     X  220.    Technic  No.  108. 


ated  chiefly  in  the   body  and   the   fundus  of  the  stomach   and   they  are 


-  THE    DIGESTIVE    ORGANS.  26/ 

named  gastric  glands  or  fundus  glands  *  (glandulae  gastricje  propriae) ; 
the  other  kind  is  confined  to  the  small  pyloric  region  and  they  are  called 
pylorus  glands.  Both  are  branched  (in  particular  the  pylorus  glands)  or 
unbranched  tubular  simple  glands  {cf.  p.  %i),  which,  individually  or  in 
groups,  open  in  pit-like  depressions  on  the  surface  of  the  mucous  mem- 
brane, the  gastric  pits  (foveola^  gastricae).  The  portion  of  the  gland 
opening  into  the  gastric  pit  is  named  neck,  the  succeeding  division,  body, 
the  blind  end,  fit ndns  or  base  (Fig.  I9i).t  Each  gland  consists  of  a 
membrana  propria  and  of  gland-cells. 

The  fundus  glands  have  two  kinds  of  cells  :  chief  cells  and  parietal 
cells.;!:  The  chief  cells  are  clear,  cubical  or  short  cylindric  elements, 
with  a  granular  protoplasm  surrounding  a  spherical  nucleus  ;  they  are 
exceedingly  frail  and  unstable.  §  The  parietal  cells  are  usually  consider- 
ably larger,  are  darker  and  of  polygonal  shape  ;  their  finely  granular 
protoplasm  encloses  a  somewhat  larger,  spherical,  often  double  nucleus. 
The  parietal  cells  are  especially  marked  by  their  affinity  for  anilin  pig- 
ments, with  which  they  stain  intensely.  The  two  kinds  of  cells  are  not 
equally  distributed.  The  chief  cells  form  the  principal  mass  of  the 
gland  follicles ;  the  parietal  cells  are  irregularly  distributed,  but  are 
especially  profuse  in  the  neck  and  the 

body.      Here   they  lie  in  a  row  beside  Portion  of  a  parietal  ceU. 

the    chief    cells;     toward    the    gland  j'i^r^    chief ceU. 

fundus  the  parietal  cells  are  pressed     Panetai  ceii  adjoin- / 

*■  mg    a    transverse -Ijj  .j land-lumen. 

out     of    the     line     of     the     chief    cells  canal  of  the  lumen.  [^^^^ 

toward  the  periphery,  however,  with- 

.  Fig.   192. — Transverse   Section  of  a   Human 

out  bemg  wholly  removed  from  the  fundus  gland.  x  240.  TechaiciNo.  los. 
lumen,  for  a  short,  simple  or  mul- 
tiple transverse  canal  (an  intercellular  secretory  capillary)  passes  out 
from  the  lumen  and  extends  between  the  chief  cells  to  the  parietal 
cell  (Fig.  192).  By  the  ajd  of  Golgi's  reaction,  which  blackens  the  se- 
cretion, it  is  most  easily  recognized  that  the  transverse  canaliculi  are 
in  connection  with  a  cluster  or  with  a  basket-like  network  of  intracellu- 

*  In  the  earlier  text-books  the  fundus  glands  were  called  peptic  glands,  a  name  based 
upon  a  function  of  the  glands  now  called  into  question. 

f  Some  authors  distinguish  the  portion  of  the  body  of  the  gland  adjoining  the  neck  as 
the  "  intercalated  division." 

J  The  theory  supported  by  different  authorities  that  the  chief  and  the  parietal  cells  are 
different  functional  pictures  of  otie  kind  of  cells  and  also  the  statement  that  during  digestion  the 
parietal  cells  multiply,  but  disappear  after  prolonged  fasting,  are  very  much  in  need  of  thorough 
investigation.  The  stomach  of  an  animal  killed  after  a  long  winter  hibernation  still  contains 
parietal  cells. 

\  The  chief  cells  are  said  to  produce  pepsin,  the  parietal  cells  hydrochloric  acid. 


268 


HISTOLOGY. 


Axial  lumen. 


Parietal  cells  with 
intracellular  se- 
cretory capillar- 
ies. 


lar  secretory  capillaries,  that  is  spread  out  within  each  parietal  cell  (Fig. 

193  and  Fig,  31,  p.  86).      The  chief  cells  have  no  intracellular  secretory 

capillaries,  but  short  intercellular 
secretory  capillaries  occur  between 
them. 

l^he  pylori ts  glands  (Fig.  194) 
are  furnished  almost  throughout  * 
with  cylindric  cells  provided  with 
a  spherical  nucleus  situated  near 
the  cell-base,  which  in  the  inter- 
mediate zone,  that  is,  the  border- 
zone  between  the  pylorus  and  the 
fundus  mucous  membrane,  so  very 
closely  resemble  the  chief  cells, 
they  have  been  compared  with 
them.  In  the  pylorus  glands  only 
short  intercellular  secretory  capil- 
laries are  found. 


Intercellular      secre- 
tory] capillaries. 


Fig.  ig3. — From  a  Section  of  a  Human  Fundus 
Mucous  Membrane.  X  230.  Portions  of  fun- 
dus glands  with  blackened  secretory  passages. 
TechnicNo.  126. 


Chief  cells. 


The  elaboration  of  secretion  in 
the  chief  cells  as  well  as  in  the  pari- 
etal cells  is  associated  with  the  for- 
mation of  granules  (p.  80).  During" 
digestion  the  chief  cells,  also  the  cells 
of  the  pylorus  glands,  are  darker,  the 
nucleus  of  the  latter  is  pushed  more  to 
the  middle  of  the  cell ;  the  secretory 
capillaries  of  the  parietal  cells,  ex- 
panded with  secretion,  are  broader- 
after  abundant  meals  the  latter  cells 
frequently  exhibit  vacuoles,  which  have  arisen  because  of  the  rapid  and 
profuse  formation  of  secretion,  that  cannot  flow  off  quickly  enough  through 
the  usual  secretory  capillaries.  In  dogs  and  cats  it  has  been  observed  that  after 
a  day's  fasting  some  of  the  parietal  cells  are  without  intracellular  secretory 
capillaries,  an  evidence  of  their  instability.  In  the  territory  of  the  cardia  and 
of  the  pylorus  are  islets  of  mucous  membrane,  which  in  their  minute  structure 
fully  agree  with  that  of  the  small  intestine. 

The  muscidaris  mticoscz  consists  of  smooth  muscle-fibers  arranged  in 
two  or  three  superposed  layers  running  in  different  directions,  from  which 
single  strands  branch  off  and  ascend  vertically  between  the  gland  follicles 
(Fig.   191). 

The  siibmucosa  is  composed  of  loose  connective-tissue  bundles 
and  elastic  fibers  and  occasionally  small  aggregations  of  fat-cells. 

*  In  man  isolated  parietal  cells  are  found;  in  animals,  e.  g.,  the  dog,  a  few  dark,  conical 
cells  occur,  that  owe  their  appearance  to  the  compression  exerted  by  neighbor  cells. 


THE    DIGESTIVE    ORGANS. 


269 


It  is  only  in  the  pyloric  region  that  two  separate  layers  of  smooth 
muscle-fibers  can  be  distinguished  in  the  vmscular  membraiie,  a  thicker 
inner  circular  and  a  thinner  outer  longitudinal  layer.  In  the  other  regions 
of  the  stomach  the  arrangement  of  the  muscle  tissue  is  very  complicated, 


Gastric  pits. 


Epithelium  of  the 
surface  cut  ob- 
Uquely,  so  that 
it  appears  to  be 
stratified. 


■Tunica  propria. 


-Pylorus  gland. 


i.  / 


Portions  of  pylorus 
glands. 


—  Solitary  nodule. 


^%- 


"^■> 


Muscularis 
mucosa. 


Fig.  194. — VzRnc.u,  Section  of  the  HuiL\N  Pylorus  Mucous  Mejibrane.     X  go-    Technic  No.  108  h. 


owing  to  the  extension  of  the  muscular  strata  of  the  esophagus  to  the 
stomach,  as  well  as  to  the  curving  of  the  organ  that  ensues  in  the  course 
of  development ;   sections  exhibit  bundles  of  fibers  extending  in  every 


270 


HISTOLOGY. 


possible  direction  (Fig.  190).  (See  further  in  the  text-books  on  macro- 
scopic anatomy.) 

The  elastic  fibers  behave  as  in  the  muscular  membranes  of  the  mid- 
gut (p.  275). 

The  serous  membrane  will  be  described  with  the  peritoneum. 

For  the  vessels  and  the  nerves  see  pp.  278—281. 

the    midgut. 
The    Duodenum  and  the   Small  Intestine. 
The  wall  of  the  midgut,  like  that  of  the  stomach,  is  composed  of 
three  membranes,  a  mucous,  a  muscular,  and  a  serous. 


Epithe- 
lium. 


Circular  muscle  )_ 
Longitudinal  muscle  ,-" 

Serosa.  t3£f^:::r  -^^ 


Fig.  195. — Vertical  Longitudinal  Section  of  the  Jejunum  or  Adult  Man.  X  i6.  The  plica  cir- 
cularis  on  the  right  supports  two  small  solitary  nodules,  that  do  not  extend  into  the  submucosa  and  of  which 
the  left  exhibits  a  germinal  center,  X.  The  epithelium  is  slightly  loosened  from  the  connective-tissue  core 
of  many  of  the  villi,  so  that  a  clear  space,  XX,  exists  between  the  two.  The  isolated  bodies  lying  near  the 
viUi  (more  numerous  to  the  left  of  the  plicae  circulares)  are  partial  sections  of  villi  that  were  bent,  therefore 
not  cut  through  their  entire  length.     Technic  No.  in. 


The  vmcosa  is  thrown  into  circular  folds,  the  pliccE  circulares,  or 
valvulas  conniventes  (Kerkring),  that  are  especially  well  developed  in  the 
upper  part  of  the  small  intestine.  In  addition  to  these  readily  percepti- 
ble structures,  the  object  of  which  is  to  increase  the  superficial  extent  of 
the   mucosa,   there   are    still  other  contrivances  serving  the  same  pur- 


THE    DIGESTIVE    ORGANS.  2/1 

pose,  that  stand  at  the  limit  of  macroscopic  perception.  These  are  the 
elevations  and  depressions  of  the  mucous  membrane.  The  former, 
the  villi,  are  present  only  in  the  duodenum  and  the  small  intes- 
tine, in  the  end-gut  of  man  they  are  wanting  ;  they  are  about  one  mm. 
high,  in  the  duodenum  of  leaf-like,  in  the  remainder  of  the  small  in- 
testine of  cylindrical  form.'''  The  depressions  begin  at  the  pylorus  and 
are  found  throughout  the  whole  length  of  the  intestine.  They  exist  in 
their  most  primitive  form  in  fishes,  where  they  originate  in  longitudinal 
parallel  folds  of  the  mucous  membrane  that  become  connected  by  small 

Tangential  sections            Artifacts, 
of  \-illi. 


b 


EpitheUum. — ~- :i  '     '.  / 

Tunica ,4-  '       .  .-^       f      ,= 

propria.  I    /     4-^  ? 


% 


Timica 
propria. 


Musoilaris- 
mucosae. 


■;Si5^^!;-" 


Submucosa.     Intestinal  crypts.  ObUque  sections  of  intestinal  crypts. 

Fig.  196. — Vertical  Section  of  the  Mucous  MEitBRANE  of  the  Jejuxum  of  Adult  Max.  X  80.  The 
empty  space,  a,  between  the  tunica  propria  and  the  epithelium  of  the  \iLIus  is  an  artifact,  the  result  of  the 
shrinking  action  of  the  fixing  fluid;  not  infrequently  within  the  space  lie  cells  that  have  been  squeezed  out 
of  the  tunica  propria.  On  its  retraction  the  epithelium  often  tears  and  then  the  \-iIlus  appears  to  have  an 
opening,  6,  at  its  apex.  The  goblet  cells  have  been  drawn  on  one  side  of  the  villus  on  the  right.  Technic 
No.  112. 

transverse  folds.  In  vertical  sections  these  shallow  depressions  appear 
as  short,  wide  sacks,  and  are  called  crypts.  In  mammals  the  cr}'pts 
are  deeper,  their  lumen  is  narrower,  and  in  rows  close  beside  one  another 

*  Toward  the  lower  end  of  the  small  intestine  the  villi  gradually  diminish  in  height  and 
frequency,  at  the  end  of  the  ileum  they  are  short,  stand  at  greater  intervals,  and  finally  on  the 
surface  of  the  ileo-cecal  valve  directed  toward  the  large  intestine  they  entirely  disappear. 


2/2 


HISTOLOGY. 


I  Goblet-cells. 


they  have  the  appearance  of  simple  tubular  glands  ;  but  they  could  only 
be  regarded  as  such  if  their  epithelial  outfit  produced  a  specific  secre- 
tion, which  is  by  no  means  the  case.*  Nevertheless,  the  name  intestinal 
glajids  (Lieberkiihn)  has  been  retained.  These  glands,  better  crypts,  of 
the  duodenum  and  the  small  intestine  are  from  o.  i  to  0.3  mm.  long.  Their 
blind  end  reaches  to  the  muscularis  mucosae. f 

The  imicous  membrane  consists  of  an  epithelium,  a  tunica  propria,  a 
muscularis  mucosae,  and  a  submucosa.  The  epithelium,  which  clothes 
the  entire  free  surface  of  the  mucous  membrane,  envelops  the  villi  and 
lines  the  crypts,  is  a  simple  cylinder  epithelium  (Fig.  17,  p.  76),  the  ele- 
ments of  which  in  their  ma- 
tured condition  consist  of  (i) 
a  granular  protoplasm,  that 
during  the  resorption  of  fat 
contains  numerous  fat-par- 
ticles, (2)  a  usually  oval  nu- 
cleus, and  (3)  a  membrane  (?). 
On  the  free  surface  of  the 
cells  there  is  a  sometimes 
homogeneous,  sometimes 
finely  striated  ciiticular  (^.^r- 
<i'^r  characteristic  of  the  intes- 
tinal epithelial  cell  [cf.  p. 7 5). 
The  regeneration  of  the 
epithelium  takes  place  only 
in  the  intestinal  crypts,  where 
by  mitotic  division  new  cells 
are  continually  formed,  which 
gradually  move  upward  and 
replace  the  cells  that  disintegrate  on  the  free  surface  of  the  mucous 
membrane.       Therefore   the   youngest    generation  of   epithelial  cells  is 


Cells  of  Paneth. 


Fig.  197. — Three  Intestinal  Crypts  from  Sections  of  the 
Ileum,  the  Two  Larger  of  Man,  the  Small  One  of  a 
Mouse.  X  390.  The  left  crypt  from  a  preparation  fixed 
in  Zenker's  fluid,  the  other  two  after  technic  No.  120. 


*  In  man  and  in  rodents  small  groups  of  granule-containing  cells  (cells  of  Paneth)  occur 
in  the  base  of  the  intestinal  crypts,  that  are  to  be  regarded  as  specific  gland-cells  (Fig.  197). 
However,  this  does  not  by  any  means  furnish  the  authority  to  consider  all  intestinal  crypts 
as  glands,  for  the  cells  of  Paneth  are  not  only  entirely  wanting  in  the  carnivora,  but  even  in 
man  it  is  only  in  the  ileum  that  they  are  invariably  to  be  found,  while  they  frequently  are  absent 
in  the  crypts  of  the  duodenum  and  are  altogether  wanting  in  those  of  the  large  intestine.  But 
even  the  existence  of  Paneth's  cells  in  the  ileum  crypts  gives  us  no  right  to  regard  the  entire 
crypt  as  gland  ;  only  the  blind  end  is  comparable  to  a  gland,  the  whole  of  the  large  division 
lying  above  being  the  equivalent  of  the  gastric  pit  of  the  stomach. 

•j-  In  a  few  instances  they  extend  beyond  into  the  submucosa ;  in  this  case  they  always  lie 
in  a  lymph  nodule.     Such  deep  crypts  are  often  found  in  the  cat. 


THE    DIGESTIVE    ORGANS. 


273 


found   in    the    crypts,    the    oldest  on  the  free  surface,  in   the   small   in- 
testine on  the  tips  of  the  villi.      Goblet-cclls  in  extremely  variable  numbers 
occur  in   the  intestinal  epithelium  ;  they  possess  an  elliptical,  not  infre- 
quently    a     chalice-like 
form,  their  upper  portion, 
that  directed  toward  the 
surface  of  the  intestine, 
is    occupied   in    varying 
extent  by  the  mucus  into 
which  the  protoplasm  is 
transformed,  the  nucleus 
with  the  remainder  of  the 
unaltered  protoplasm  lies 
at  the  base  of  the  cell ;  a 

cuticular  border  is  wanting,  in  place  of  which  a  sharply  defined  circular 
orifice  is  found  (Fig.  198  A)  through  which  the  mucus  is  poured  out  on 


Fig.   I 


-Intestinal    Epithelium. 


X  560.  .4.  Isolated  goblet- 
cells  of  a  rabbit,  .x.  Escaping  mucus.  Technic  No.  no  a. 
B.  From  a  section  of  the  mucous  membrane  of  the  human  in- 
testine, b.  A  goblet-cell  between  cylinder  cells.  Technic 
Xo.  III. 


Epithelium. 


5 


Tunica  propria. 


Portion  of  a  capillary 
blood-vessel. 


Cuticula. 


Xucleus  of  a'wandering 
leucocyte. 


Tangential  section  of  a 
goblet-cell. 


Mucoid  zone  of  a  goblet - 
ceU. 


Xucleus  of  a  smooth  muscle-fiber. 


Lacteal  or  central  space. 


Fig.  199. — LoNGiTrDiN.\L  Section  through  the  Apex  of  the  Villus  of  a  Dog.     xr36o.     The  goblet-cells 
contain  the  less  mucus  the  nearer  they  lie  to  the  summit  of  the  villus.     Technic  i\o.  112. 


the  surface  of  the  intestine.      The  goblet-cells  are  derived  from  the  ordi- 
nary epithelial  cells  of  the  intestine.      In  suitable  conditions  each  young 


18 


274 


HISTOLOGY. 


young  intestinal  epithelial  cell  can  become  a  goblet-cell*  and  produce 
mucin. 


Intestinal  crypts.. 


Duodenal  gland  in  the  tunica 
/  propria. 


intestinal  crypts.^ ^^     c  l^^*JK^>!^  ^^^^ 

Epithelium.     Villi  '^^^^MM^I'^^y'^^    circularis.      Duodenal  glands  in  the 

V  ,  .r^      ^5  y  /  Fat.  submucosa 


A    i  ,, 

Tunica  propria.  X;^l\l^\^^^^W^' -^^S^^^^ 


^i 


Muscularis  mucosae. —  r^^^^^S^MiSAJ"  ^  }^<yv^k\^  \  6^/. 
Submucosa. —  ■-  -~^£2'i« 

Stratum  of  circular 

muscle. 

Stratum  of  longitud- 

inal  muscle. 

Connective  tissue. — 


Intestinal  crypts. 


WM'M^ 


Fig.  200. — Vertical  Longitudinal  Section  of  the  Human  Duodenum.     X  i6.    Technic  No.  log. 

The  separate  phases  of  secretion  appear  in  regular  sequence  and  so 

that  the  later  stages  are  always  higher, 
near  the  tips  of  the  villi  (Fig.  199), 
than  the  initial  stages,  which  are  found 
in  the  intestinal  crypts. 

Between  the  epithelial  cells  mi- 
gratory leucocytes  from  the  underlying 
tunica  propria  are  found  in  varying 
number. 

The  tunica  propria  forms  the  bodies 
of  the  villi  and  fills  the  spaces  between 
the  intestinal  glands,  at  the  blind  end 
of  which  it  is  arranged  in  a  thin  stra- 
tum. It  consists  chiefly  of  reticular  and 
fibrillar  connective  tissue  intermingled 
with  elastic  fibers,  that  contains  a 
widely  varying  quantity  of  leucocytes 
{cf.  p.  145). 

The  muscularis  mucosce  consists  of 
an  inner  circular  and  an  outer  longitu- 
dinal layer  of  smooth  muscle-fibers. 
Fibers  derived  from  the  muscularis 
mucosae  ascend  within  each  villus 
nearly  to  its  apex.  Their  contraction  effects  a  shortening  of  the  villus. f 
The  elastic  fibers  behave  as  in  the  muscle  membrane. 

*  In  regard  to  the  mode  in  which  the  goblet-cells  produce  secretion,  see  p.  81. 
f  Cf.  Technic  No.  no,  p.  301. 


of  duodenal  gland-sacs. 


Fig.  201. — From  a  Section  of  a  Human  Duo- 
denum. X  240.  Only  the  lower  half  of 
the  mucosa  and  upper  half  of  the  submu- 
cosa are  sketched.  A  large  portion  of 
the  duodenal  gland  lies  above  the  muscularis 
mucosae.    Technic  No.  109. 


THE    DIGESTIVE    ORGANS.  2/5 

The  siibinucosa  consists  of  loose  fibrillar  connective  tissue  with  a 
sparing  admixture  of  elastic  fibers  ;  in  the  territory  of  the  duodenum  it 
contains  compound  alveolo-tubular  glands,  from  0.2  to  3.4  mm.  in  size, 
the  duodenal  glands  (Brunner).*  In  man  they  lie  densely  crowded  at 
the  sphincter  of  the  pylorus,  but  diminish  in  number  down  therefrom. 
In  the  vicinity  of  the  cystic  duct  they  are  again  more  profuse ;  toward 
the  end  of  the  duodenum  they  vanish  entirely.  Their  excretory  duct, 
clothed  with  simple  cylinder  epithelium,  pierces  the  muscularis  mucosae 
and  opens  either  into  the  base  of  an  intestinal  crypt  or,  running  parallel 
with  the  latter  in  the  tunica  propria,  on  the  inner  surface  of  the  intestine. 
The  walls  of  the  alveolo-tubules  are  formed  of  a  structureless  mem- 
brana  propria  and  of  cylindric  gland-cells,  resembling  the  cells  of  the 
pylorus  glands. 

The  muscle  tunic  of  the  intestine  consists  of  an  inner,  robust  circu- 
lar and  an  outer,  slighter  longitudinal  stratum  of  smooth  muscle-fibers. 
Numerous  elastic  fibers  lie,  not  only  on  the  outer  and  inner  surfaces  of 
both  muscle  strata,  but  also  within  the  strata.  Their  number  stands  in 
direct  relation  to  the  thickness  of  the  musculature. 

For  the  structure  of  the  serosa,  see  the  Peritoneum,  p.  295. 

THE    ENDGUT. 

I.  The  Large  Intestine. 

The  wall  of  the  large  intestine  likewise  consists  of  a  mucous  mem- 
brane, a  muscular  membrane  and  a  serosa. 

The  mucous  membrane  is  smooth,  villi  are  wanting,  and  the  crypts 
are  twice  as  long  (0.4  to  0.6  mm.)  as  those  of  the  small  intestine.  The 
epithehum,  tunica  propria,  and  muscularis  mucosae  are  the  same  as  those 
of  the  small  intestine,  with  which  they  also  agree  in  their  microscopic 
structure  and  in  the  regeneration  of  the  epithelium.  The  glands  contain 
a  relatively  large  number  of  goblet-cells. t 

*  The  bodies  of  the  duodenal  glands  do  not  all  lie  exclusively  in  the  submucosa ;  often 
portions,  in  fact  near  the  end  of  the  duodenum  entire  bodies  of  duodenal  glands  are  found  in 
the  territory  of  the  tunica  propria.  In  the  cat  duodenal  glands  in  process  of  atrophy  are  fre- 
quently found. 

t  The  reason  for  this  lies  in  the  fact  that  the  young  epithelial  cells  originating  in  the 
glands  of  the  small  intestine  move  more  rapidly  to  the  surface  ;  for  the  superficies  of  the  small 
intestine,  so  greatly  augmented  by  the  villi,  requires  a  larger  reparative  supply  to  replace  the 
cells  perishing  there ;  therefore  the  elaboration  of  mucus  often  does  not  take  place  within  the 
crypts,  but  first  begins  in  the  cells  on  the  villi.  In  the  large  intestine,  where  the  villi  are  absent, 
the  transit  to  the  surface  takes  place  slowly  and  the  cells  have  time  to  produce  secretion  during 
their  sojourn  in  the  crypts.  It  is  this  that  gave  rise  to  the  erroneous  impression  that  the  glands 
of  the  small  intestine  yield  a  serous  fluid,  the  glands  of  the  large  intestine  mucus. 


2/6 


HISTOLOGY. 


The  muscular  coat  of  the  large  intestine  consists  besides  elastic  fibers 
of  an  inner  annular  and  an  outer  longitudinal  layer  of  muscle  ;  the  latter 
is  well-developed  only  within  the  territory  of  the  taenia,  being  extremely 
thin  in  the  intervals, 
of  the  small  intestine. 


The  serosa  agrees  in  its  minute  structure  with  that 


The  vermiform  process  of  man  is  characterized  by  a  large  number  of 
round,  in  old  persons  flat,  lymph  nodules  (see  below)  and  is  in  many  cases — 
25  per  cent. — partially  obliterated;  this  process  occurs  with  increasing  frequency 


Glands  (crypts). 


&^-.:vj|>.::--,'-  \    -.■ 


■•t;i:;ii^^iMPI^-- 


r<r_ 

-  Epithe- 
lium. 

pro- 
pria. 

Submu- 
cosa. 


Fat-cells. 


Solitary    nodule    with    germinal    center. 


Fig.  202. — Vertical  Section  of  the  Mucous  Membrane  of  the  Descending  Colon  of  Adult  Man.  X  80. 
Compare  the  length  of  the  glands  with  those  of  the  small  intestine  (Fig.  196),  that  are  from  the  same  indi- 
vidual and  drawn  under  the  same  magnification.     Technic  No.  114. 

in  advanced  age — in  50  per  cent,  of  persons  over  60  years.  The  obliteration 
is  not  the  result  of  a  pathologic  process,  but  the  effect  of  the  elsewhere  familiar 
involution.  Epithelium  and  glands  perish,  lymph  nodules  disappear,  and  the 
tunica  propria  is  transformed  into  an  axial  connective-tissue  strand,  that  is 
enclosed  in  the  unaltered  submucosa  and  muscularis.  These  post-embryonal 
processes  must  not  be  confused  with  the  kataplastic  changes  in  the  intestinal 
glands,  occurring  from  the  5th  to  the  6th  embryonal  month,  which  so  far  have 
been  observed  only  in  man. 


2.    The    Rectum. 
In  composition  and  structure  the  rectum  in  general  agrees  with  the 
large  intestine,  but  is  distinguished  by  its   longer  glands  (0.7  mm.)  and 


THE    DIGESTIVE    ORGANS. 


277 


by  a  thick  longitudinal  layer  of  muscle.  At  the  upper  end  of  the 
columnar  rectales  begins  the  transition  of  the  mucous  membrane  into 
the  skin  ;  instead  of  the  simple  cylindrical  epithelium,  a  powerful  strati- 
fied squamous  epithelium  appears,  which  covers  a  tunica  propria  with 
vascular  papillae.  The  intestinal  glands  may  be  traced  for  a  short  dis- 
tance into  the  territory  of  the  stratified  squamous  epithelium,  but  farther 
on  they  are  wholly  wanting.  The  columnae  rectales  contain  smooth 
muscle-fibers. 


Intestinal  glands. 


of  the  muscularis. 

Fig.  203. — Transverse  Section  of  a  Patch  of  Peyer  of  the  Small  Intestine  of  a  Cat.     The  crests  of  four 
nodules  were  not  within  the  plane  of  the  section.     X  10.     Technic  Xo.  113. 


The  Lymph  Nodules  of  the  Stomach  and  the  Intestines. 

It  has  been  previously  mentioned  (p.  145)  that  the  tunica  propria  of 
the  mucous  membranes  contains  leucocytes  in  variable  numbers,  either 
distributed  as  diffuse  adenoid  tissue  or  balled  together  in  circumscribed 
masses.  In  the  latter  case  they  form  nodules  from  o.  i  to  2.5  mm.  large, 
which  stand  isolated,  as  the  solitary  nodules,  or  united  in  groups  as  the 
agminate d  nodules. 

The  solitary  nodidcs  ("  solitary  follicles  ")  occur  in  greatly  varying 
number  in  the  gastric  mucous  membrane,  in   larger  number  in  the  intes- 


2/8 


HISTOLOGY. 


Epithelium. 


//S««. 


0©0«>    'i 


O  O  ( 


tines.  They  usually  possess  an  oval  form  and  in  the  beginning  of  their 
development  always  lie  in  the  tunica  propria;  *  their  summit  extends  up 
close  under  the  epithelium,  their  base  is  directed  toward  the  muscularis 
mucosae.  With  progressive  growth  (in  cats  at  the  time  of  birth)  they 
break  through  the  muscularis  mucosae  and  expand  in  the  submucosa, 
where  the  loose  tissue  offers  but  little  resistance.  The  part  of  the  nodule 
lying  in  the  submucosa  has  a  spherical  form  and  soon  becomes  consider- 
ably larger  than  the  division 
lying  within  the  tunica  propria. 
Therefore  the  matured  solitary 
nodules  are  pyriform,  with  the 
small  end  turned  toward  the 
epithelium.  Where  the  no- 
dules are  situated  the  villi  are 
wanting  and  the  crypts  are 
pushed  aside.  The  solitary 
nodules  are  composed  of  ade- 
noid tissue  and  usually  contain 
a  germinal  center  (p.  146). 
The  young  leucocytes  formed  in  them  in  part  pass  into  the  neighbor- 
ing lymph-vessels  and  in  part  wander  through  the  epithelium  into  the 
intestinal  cavity.  The  cylinder  epithelium  covering  the  apex  of  the 
nodules  always  contains  leucocytes  in  course  of  migration  (Fig.  204). 

The  agminated  nodules  (patches  of  Peyer)  are  groups  of  from  ten  to 
sixty  nodules  that  lie  side  by  side,  never  over  one  another,  each  of 
which  has  the  structure  of  a  solitary  nodule.  Occasionally  the  out- 
line of  an  individual  nodule  is  altered  by  the  pressure  of  adjacent 
nodules  (Fig.  203).  They  principally  occur  in  the  lower  portion  of  the 
small  intestine,  always  on  the  side  opposite  to  the  attachment  of  the  mesen- 
tery, either  distinctly  isolated  from  one  another  or  transformed  into  a  diffuse 
mass  of  leucocytes,  in  which  only  the  germinal  centers  can  be  distin- 
guished.   This  is  not  infrequently  the  case  in  the  vermiform  process  of  man. 


Fig.  204. — From  a  Section  of  the  Small  Intestine  of  a 
Seven-day-old  Kitten.  X  250.  Crest  of  a  solitary 
nodule.  The  epitheUum  on  the  left  contains  many 
wandering  leucocytes.  The  epithelium  on  the  right  con- 
tains but  three  leucocytes.     Technic  No.  113. 


The  Blood-vessels  of  the  Stomach  and  of  the  Intestines. 

The  blood-vessels  of  the  stomach  and  of  the  large  intestine  have  a 
precisely  similar  distribution,  which  is  modified  in  the  small  intestine  by 
the  presence  of  the  villi.  In  the  stomach  and  in  the  large  intestine 
the  entering  arteries  first  give  off  small  branches  to  the  serosa,  then 
pierce  the  muscularis,  which  they  supply,  and  then  in  the  submucosa 


*This  is  also  their  nsual  seat  in  the  human  small  intestine,  while  in  the  large  intestine 
they  also  extend  into  the  submucosa  (f/.  Fig.  195  with  Fig.  202). 


THE    DIGESTIVE    ORGANS. 


279 


form  a  network  extending  parallel  to  the  surface.  From  this  small 
twigs  ascend  through  the  muscularis  mucoScX  into  the  tunica  propria, 
where  at  the  base  of  the  glands  they  form  another  network 
spread  parallel  to  the  surface.  Fine  capillaries  (from  4. 5  to  9  fx  wide) 
develop  from  the  latter,  form  plexuses  that  envelop  the  glands  and 
pass  into  capillaries  twice  as  wide  (from  9  to  18  u),  which  latter  form  a 
plexus  that  lies  wreath-like  about  the  mouths  of  the  glands.  Venules 
take  their  origin  from  the  wide  capillaries,  which  without  taking  up 
other  branches  pass  vertically  down  between  the  gland  tubules  and  open 
into  a  venous  plexus  spread  parallel  to  the  surface  in  the  tunica  propria  ; 
in  their  further  course  the  veins  run  alongside  the  arteries.     The  veins 


Veins. 


Tunica  propria  /t^-X  V 


*.«»-„  ,-..-'^5^0C£^:^7'  '- 


Muscularis  mucosK. 


Submucosa. 


Fig.  205. — Vertical  Section  of  the  Mucous  Membrane  of  the  Human  Jejunum.    X  so.    The  blood-vessels 
are  injected  with  Berhn  blue.     The  vein  of  the  first  villus  on  the  left  is  cut  transversely.     Technic  No.  ii6. 

arising  from  the  venous  plexus  in  the  submucosa  are  furnished  with  valves 
to  the  point  where  they  empty  into  the  approaching,  parallel  collecting 
veins  of  the  intestine.  The  remaining  branches  and  the  trunk  of  the 
portal  vein  are  without  valves. 

In  the  small  intestine  only  the  arteries  supplying  the  crypts  are  dis- 
tributed in  the  same  manner  as  in  the  large  intestine.  The  villi  are 
provided  with  one  artery  (several  when  the  villus  is  broad),  which  lies 
opposite  the  vein  ;  from  the  former  capillaries  arise  that  lie  close  under 
the  epithelium  and  obliquely  or  vertically  to  the  long  axis  of  the  villus 
pass  into  the  veins.*  The  further  course  of  the  veins  is  the  same  as  in 
the  larg-e  intestine. 


*  The  distribution  is  the  same  in  the  dog,  but  in  the  rabbit  and-the  guinea-pig  the  arteries 
going  to  the  villi  break  up  into  fine  branches  that  run  to  the  base  of  the  villus  and  then  form  a 


28o  HISTOLOGY. 

The  duodenal  glands  are  enveloped  in  a  capillary  plexus  which  is 
supplied  by  the  blood-vessels  of  the  submucosa. 

The  lymph  nodules  ("follicles")  are  surrounded  by  a  superficial 
capillary  network,  from  which  fine  capillaries  extend  into  the  interior  ; 
often  these  do  not  penetrate  to  the  center,  in  which  case  a  non-vascular 
spot  exists  in  the  middle  of  the  nodule. 

The  Lymph-vesselS  of  the  Stomach  and  of  the  Intestines. 

The  lymph-  (chyle)  vessels  of  the  stomach  and  of  the  large  intestine 
begin  in  the  mucous  membrane  as  blind  capillaries,  about  30  //  wide,  and 
descend  between  the  gland  follicles.  In  the  mucous  membrane  of  the 
small  intestine  the  lymph-vessels  begin  in  the  axis  of  the  villi ;  in  cylin- 
drical villi  they  are  simple,  in  leaf-shaped  villi  multiple  ducts  (from  27  to 
36  ij.  wide)  closed  at  their  upper  end,  and  represent  the  "  central  space  " 
of  the  villus  (Fig.  199).  All  these  vessels  descend  to  a  narrow-meshed 
capillary  plexus  lying  at  the  base  of  the  glands  and  extending  parallel  to 
the  surface,  which  communicates  by  numerous  anastomoses  with  a  wide- 
meshed  horizontal  plexus  in  the  submucosa  ;  the  lymph-vessels  proceed- 
ing from  this  network  are  provided  with  valves,  penetrate  the  muscular 
coat  and  here  take  up  the  efferent  vessels  of  a  plexus  lying  between 
the  circular  and  longitudinal  muscular  strata.  This  plexus  is  called 
the  interlaminar  lymph-vessel  plexus,  and  takes  up  the  numerous  lymph 
capillaries  of  both  muscular  layers.  Beneath  the  serosa  the  lymph-ves- 
sels ("  subserous  lymph-vessels  ")  run  to  the  attachment  of  the  mesen- 
tery and  then  pass  onward  between  its  folds. 

The  course  of  the  lymph-vessels  just  described  is  modified  in  the 
mucosa  of  certain  localities.  These  places  are  the  patches  of  Peyer  ; 
the  nodules,  which  never  contain  lymph-vessels,  press  aside  the  capillaries, 
which  run  in  the  interstices  between  them,  as  canals  diminished  in  num- 
ber, but  increased  in  caliber.  It  is  probable  that  the  lymph-sinuses  of  the 
rabbit  (p.  146,  remark*)  are  nothing  else  than  such  immensely  widened, 
flattened  capillaries. 

The  Nerves  of  the  Stomach  and  of  the  Intestines. 
The  numerous  nerves,  mainly  consisting  of  nonmedullated,  sympa- 
thetic fibers,  form  a  plexus  beneath  the  serosa,  then  pierce  the  longitu- 
dinal layer  of  the  muscular  tunic  and  spread  out  between  this  and  the 

capillary  network  that  lies  close  under  the  epithelium.  At  the  summit  of  the  villus  the  capil- 
laries open  into  a  small  venous  trunk,  that  in  the  course  of  its  vertical  descent  takes  up  the  capil- 
laries surrounding  the  mouths  of  the  glands.  I  have  found  the  same  arrangement  in  the  broader 
villi  of  man. 


THE    DIGESTIVE    ORGANS. 


2«1 


circular  muscle  la}-er  in  a  conspicuous  network,  the  plexus  niyentericus 
(Auerbach),  which  is  furnished  with  numerous  groups  *  of  multipolar  gan- 
glion cells,  usually  found  at  the  nodal  points  of  the  network.  The  meshes 
of  the  plexus  are  polygonal.  From  this  network  bundles  of  nonmedul- 
lated  nerve-fibers  are  given  off,  usually  at  right  angles,  part  of  which  sup- 
ply the  longitudinal  and  circular  strata  of  the  muscular  tunic,  part  of 
which  pierce  the  latter  and  enter  the  submucosa.  In  the  musculature  the 
nerves  form  a  rich,  rectangular-meshed  network,  from  which  nerve-fibers 
turn   aside  and  after    repeated  division  approach  the  muscle-fibers,  on 


A 


B 


Fig.  206. — .-1.  Surface  View  of  the  Plexus  Myentericus  of  ax  Infant.     X  50.     g.  Groups  of  ganglion 

cells  ;  r,  layer  of  circular  muscle-fibers,  recognized  by  their  rod-shaped  nuclei.     Technic  No.  117  a. 

B.  Surface  View  of  the  Plexus  Submucosus  of  the  same  Infant.     X  so.    g.  Groups  of  ganglion  cells  ; 

b,  blood-vessel  shimmering  through  the  overlying  tissue.     Technic  No.  117  6. 


which  (not  within)  they  terminate  in  free,  slightly  swollen  endings.  The 
nerves  that  go  to  the  submucosa  there  form  a  second,  delicate  plexus, 
Xhc  plexus  subnmcosus  (Meissner),  the  meshes  of  which  are  narrower  and 
the  groups  of  ganglion  cells  f  smaller.  From  this  spring  numerous  fibers, 
which  enter  the  tunica  propria  and  in  part  weave  a  nervous  net  about  the 
glands,  in  part  enter  the  villi,  where  they  terminate  free  in  the  paren- 
chyma of  the  villus  or  close  beneath  the  epithelium,  without  connection 
with  the  epithelial  cells. 

*  These  groups — small  ganglia — behave  similarly  to  the  sympathetic  ganglia  and  contain 
chiefly  cells  of  type  i  [cf.  p.  218). 

f  Their  elements  belong  mainly  to  type  ii  (p.  218)  and  with  their  dendrites  may  reach  to 
beneath  the  epithelium. 


282 


HISTOLOGY. 


A   plexus   corresponding   to   the   plexus   myentericus   also    occurs 

between  the  layers  of  the  muscular  mem- 
brane of  the  esophagus. 

The  Pancreas. 

The  pancreas  is  for  the  smaller  part 
a  tubular,  for  the  greater  part  an  alveolar 
gland  {cf.  p.  84).  Its  canal  system  con- 
sists of  an  excretory  duct,  the  branches 
of  which  do  not  lead  into  secretory 
tubes, — these  are  wanting, — but  directly 
into  very  long  intercalated  tubules,  that 
dividing  repeatedly  pass  into  mostly 
short  end-pieces. 

The  excretory  ducts,  the  pancre- 
atic duct  (Wirsungi)  and  the  acces- 
sory pancreatic  duct  (Santorini),  are 
composed  of  a  simple  cylindric  epithe- 
lium and  of  connective  tissue,  which 
latter  is  denser  beneath  the  epithelium, 
looser  toward  the  periphery.  The  chief 
excretory  duct  and  its  coarser  branches  carry  in  their  walls  small  glands, 


End- 
pieces. 


Fig.    207. — Scheme   of   the   Human    Pan 
CREAS.    X,  tubular  end-piece. 


Cells  of 
the  end- 
piece. 


f"        f    Inter- 
-~^^-^^calated 
tubule. 


Centroacinar  cells. 


.4. 


Zymogen  granules. 


Fig.  208. — From  Sections  of  a  Human  Pancreas.  X  500.  In  section  A  the  granules  are  wanting,  the  elements 
of  the  intercalated  tubule  are  flat  and  dark  ;  in  section  B  the  granules  are  distinct,  the  cells  of  the  inter- 
calated tubule  are  cubical  and  clear.    Technic  No.  119. 

the  elements  of  which  resemble  mucous  cells.*     The  cylinder  epithelial 
cells  of  the  smaller  branches  steadily  decrease  in  height  and  finally  pass 


"  Regarding  the  musculature,  see  remark  *,  p.  287. 


THE    DIGESTIVE    ORGANS. 


283 


into  the  longitudinally  disposed  cubical  or  plate-like  cells  of  the  interca- 
lated tubules.  These  cells  of  the  intercalated  tubules  do  not  directly  an- 
nex themselves  to  the  epithelium  of  the  end-pieces,  as,  for  example,  is  the 
case  in  the  submaxillary  gland  (Fig.  168,  _ 

right),  but  as  the  so-called  centroacinar 
cells  shove  themselves  into  the  interior 
of  the  end-pieces,  whereby  they  come  to 
lie  upon  the  inner  surface  of  the  secreting 
cells  *  (Fig.  208).  The  latter  are  small 
conical  cells,  that  in  the  zone  directed 
toward  the  lumen  contain  numerous 
highly  refracting  granules,  the  zyviogcu 
graimlcs,  precursors  of  the  secretion.  In 
fresh  preparations  they  are  visible  even 
with  relatively  low  magnification  (Fig. 
232) ;  the  clear  peripheral  division  of 
the  cell  contains  the  round  nucleus.  The 
relative  proportions  of  the  granular  and  clear  zones  vary  according  to  the 
functional  state  of  the  cell.  In  the  beginning  of  digestion  the  granules  dis- 
appear, while  the  clear  zone  of  the  cell  becomes  larger.  Then  the  granular 
zone  again  enlarges,  to  such  extent  that  it  occupies  nearly  the  entire  cell.  In 


Fig.  2og. — Transverse  Section  of  a  Gland- 
tubule  OF  THE  Pancreas  of  Necturus  ; 
showing  zymogen  granules.  X  400. — 
{Schaper.) 


Intercal- 
ated 

Centroacinar  cells. 

Cells  of 
the  end- 

piece.    \ 

1 

;    piece. 

Intercellular 
secretory 
capillary. 

Fig.  210. — A.  From  a  Section  of  the  P.\ncrea3  of  Adult  Man.     X  320.     Technic  No.  126. 
B.  ScHEM.iTic  Elaboration  of  the  Right  Lower  Portion  of  .1. 

the  fasting  state  the  two  zones  are  of  equal  size  (r/".  p.  80). f  Intercellular 
secretory  capillaries  extend  from  the  axial  lumen  between  the  gland-cells, 
without  reaching  to  the  membrana  propria  ;  where  the  centroacinar  cells 
shut  off  the  gland-cells  from  the  central  lumen  the  latter  pour  their  secre- 


*  Owing  to  this  the  microscopic  picture  is  a  very  complicated  one  and,  with  the  lumen 
not  always  visible  and  the  many  unavoidably  oblique  sections,  very  difficult  to  understand  {cf. 
in  particular  Fig.  20S  B).     The  centroacinar  cells  cannot  be  demonstrated  in  all  end-pieces. 

I  The  cells  of  the  intercalated  tubules  also  show  changing  states  (Fig.  20S). 


284 


HISTOLOGY. 


tion  into  secretory  capillaries  which  penetrate  between  the  centroacinar 
elements  and  open  into  the  axial  lumen  (Fig.  210  B). 

The  blood-  and  lymph-vessels,  as  well  as  the  nerves,  behave  as  in 
the  glands  of  the  oral  cavity. 

In  the  pancreas  are  found  groups  of  epithelial  cells  arranged  in  solid 
cords,  varying  in  number,  always  small, — measuring  up  to  0.3  mm., — called 
t'ht  inte7'hihular  cell-groups,  that  usually  are  separated  from  the  remaining  tissue 
of  the  pancreas  by  a  scanty  amount  of  connective  tissue  poor  in  elastic  fibers. 
They  are  penetrated  by  wide  capillaries  and  have  a  certain  resemblance  to  liver 
tissue.  Gland  lumina  have  not  yet  been  demonstrated  in  mammals.  The 
meaning  of  these  structures  is  still  uncertain. 


Artery. 


Portal  vein. 


Ramification  of  the 
excretory  duct. 


End  pieces 


Fig.  211. — Scheme  of  an  Ordinary  Compound 
Tubular  Gland.  In  lobule  3  only  the  ramifica- 
tions of  the  excretory  duct,  without  the  end-pieces, 
are  sketched. 


Capillaries. 


Vein. 


Fig.  212. — Scheme  of  the  Liver.  In  lobule  1  only 
the  direction,  in  2  only  the  branching,  of  the  end- 
pieces  is  sketched  ;  in  3  only  the  excretory  ducts 
are  drawn. 


The    Liver. 

The  canal  system  of  the  liver  consists  of  an  excretory  duct  (the 
hepatic  duct)  the  ramifications  of  which  pass  into  end-pieces.  Separate 
divisions  of  the  excretory  system,  corresponding  to  secretory  tubes  or 
to  intercalated  pieces,  cannot  here  be  distinguished.  The  liver  is  a 
compound  tubular  gland  *  ;  this  structure  is  recognized  with  difficulty 
on  account  of  the  following  peculiarities  : 

I.  In  the  other  glands  f  the  end-pieces  are  convoluted  (Fig.  21 1), 
in  the  liver  they  are  nearly  straight  (Fig.  212). 

*In  this  form  the  organ  persists  apparently  only  in  one  vertebrate  (myxine)  ;  in  other 
vertebrates  it  changes  during  embryonal  life  to  a  net-like  gland,  by  the  union  of  its  branched 
tubules. 

f  In  the  entire  ensuing  comparison  the  compound  tubular  glands  are  meant. 


THE    DIGESTIVE    ORGANS. 


285 


2.  In  the  other  glands  the  end-pieces  course  in  every  possible 
direction  and  surround  on  all  sides  the  ramifications  of  the  excretory 
duct  ;  hence  the  latter  lie  in  the  interior  of  the  gland  lobules  (p.  85). 
In  the  liver  the  end-pieces  run  in  a  definite  direction,  toward  the  axis 
of  the  lobule  ;  all  ramifications  of  the  excretory  duct  lie  external  to  the 
gland  lobules  {cf.  Fig.  211  with  Fig.  212). 

3.  In  the  majority  of  other  glands  the  end-pieces  terminate  blindly, 
without  anastomosing  with  one  another,  in  the  liver  the  end-pieces  are 
freely  connected  with  one  another  and  form  a  net  (Fig.  212,  2). 
Hence  the  term  "end-piece  "  is  inadequate,  for  blind  ends  have  not  yet 
been  with  certainty  established  in  the  liver;  instead  of  the  name  "end- 
piece,"  the  phrase  "  trabecula  of  hepatic  cells"  or  "hepatic  trabecula  " 
will  be  adopted  in  the  description  of  the  liver. 

Gland  lumen  (bile 
capillary) . 


Gland  lumen.    — 


Blood- 
~^      vessels. 

Fig.  213. — Scheme  of  .a    Segment    of    the    End- 
piece  OF    .AN  ORDINARY  TUBULAR    GlAND. 


Fig.  214. — Scheme  of  a  Segment  of  an  End- 
piece  (Hep.atic  Trabecula)  of  the  Liver. 
The  Union  with  neighbor  Trabecul.e  is 
here  not  taken  into  account. 


4.  In  other  glands  the  arteries  and  veins  proceed  together  with  the 
ramifications  of  the  excretory  duct  and  like  these  lie  in  part  within  the 
lobule  (Fig.  211,3).  If'  the  liver  the  portal  vein,  which  corresponds  to  the 
artery  of  other  glands,  follows  the  branches  of  the  excretory  duct  and 
like  these  lies  external  to  the  lobule.  But  the  veins  course  independently 
of  the  branches  of  the  portal  vein  ;  even  their  origin  lies  in  the  interior 
of  the  lobule  (Fig.  212). 

In  addition  to  these  relatively  gross  distinctions  there  are  minute 
differences. 

5.  In  other  glands  the  axial  lumen  of  the  end-piece  in  cross-sec- 
tion is  surrounded  by  many  gland-cells — six  or  more  (Fig.  213)  ;  in  the 
liver  by  only  two  gland-cells  (Fig.  214).    This  difference  is  conditionated 


286 


HISTOLOGY. 


by  the  relatively  large  size  of  the  gland-cells  (hepatic  cells),  on  the  one 
hand,  and  by  the  extreme  narrowness  of  the  gland  lumina  of  the  liver,  on 
the  other  hand  ;  two  hepatic  gland-cells  are  exactly  enough  to  circum- 
scribe the  lumen. 

6.  In  other  glands  each  gland-cell  attains,  to  contact  with  a  blood- 
vessel only  on  one  side  (Fig,  213);  in  the  liver  each  hepatic  cell  has 
several  sides  touching  blood-vessels  (Fig.  214),  a  circumstance  likewise 
brought  about  by  the  size  of  the  hepatic  cells. 

All  these  peculiarities  would  not   so   greatly  obscure  the   tubular 

gland  character  of  the  liver  were 
it  not  for  the  existence  of  a  still 
greater  difference  : 

7.  In  other  glands  the  cells 
of  the  end-pieces  are  not  in  direct 
contact  with  the  cells  of  neighbor 
end-pieces,  they  are  always  sepa- 
rated by  connective  tissue,  the 
membrana  propria  and  so  forth 
{cf.  e.  g.  Fig.  30,  p.  85);  in  the 
liver  the  cells  of  neighboring  hep- 
atic trabeculae  come  into  immedi- 
ate contact  on  several  sides  and 
these  contiguous  surfaces  likewise 
embrace  a  gland  lumen  ;  which 
figure  215  may  serve  to  elucidate. 
Cross-sections  of  four  trabeculae  of  liver  cells  are  drawn.  The  first,  con- 
sisting of  the  cells  i  and  2,  touches  directly  on  the  second  trabecula, 
consisting  of  the  cells  a  and  b.  i  and  2  enclose  a  gland  lumen 
(i),  likewise  a  and  b.  Between  the  contiguous  surfaces  of  i  and  a 
there  is  also  a  lumen  (11).  Thus  the  gland-cells  of  the  liver,  not  only 
on  one  surface  but  on  several  surfaces  touch  on  lumina ;  these  lumina 
may  be  united  with  one  another  by  lateral  branches  that  run  between 
the  gland-cells  and  thereby  form  actual  meshes.  The  right  half  of  the 
figure  shows  such  a  mesh  ;  it  embraces  the  cross-section  of  a  blood-vessel 
and  therefore  may  be  named  vasozonal  mesh,  in  contradistinction  to 
meshes  that  girdle  a  single  liver  cell  and  are  called  cytozonal  meshes. 
The  arrangement  by  which  the  gland-cells  of  the  liver  are  embraced 
on  different  sides  by  gland  lumina  also  occurs  in  other  gland-cells,  for 
example,  in  the  serous  cells  of  the  salivary  glands,  that  are  surrounded  by 
an  entire  network  of  secretory  capillaries  (Fig.  169)  ;  the  gland  lumina 
of  the  liver  may  be  directly  compared  with  the   secretory  capillaries  of 


Bile  capillanes 


Blood  capillaries. 

Fig.  21S. — Section  of  a  Rabbit's  Liver.  X  570. 
The  outliiies  were  made  with  a  camera  lucida.  The 
dark  nuclei  of  the  blood  capillaries  and  the  different 
shading  of  the  hepatic  trabecule  are  schematic. 
The  section  passes  through  ■  the  hepatic  trabecule 
1/2  and  a/h  in  such  wise  that  the  gland-cells  are 
halved  ;  through  the  trabeculee  3/4  and  c/ d  ex- 
actly between  contiguous  gland-cells.  The  cells  3,  4 
and  c,  d  exhibit  their  surface  to  the  observer. 


THE    DIGESTIVE    ORGANS. 


287 


Trabecule  of 
hepatic  cells. 


Central  vein. 


Other  glands  and  named  bile  capillaries.  But  while  in  other  glands 
the  secretory  capillaries  open  into  a  larger  axial  chief  lumen,  such  axial 
lumina  are  wanting  in  the  domain  of  the  hepatic  lobule  ;  the  bile  capil- 
laries open  at  the  peripher}-  of  the  lobule  directK-  into  the  interlobular 
bile-ducts. 

Tlic  microscopic  strncUire  of  the  liver.  The  main  excretor}'  duct,  the 
hepatic  duct,  and  its  larger  branches  consist  of  a  simple  stratum  of  cylin- 
der epithelium,  occasional!}-  containing  goblet-cells,  and  of  connective 
tissue  separated  into  a  tunica  propria  and  a  submucosa.  The  tunica  pro- 
pria is  the  carrier  of  the  glands  of  the  bile-duct,  chiefly  short,  pear- 
shaped  follicles  clothed  with  mucous 
o-land-cells,  and  of  isolated  longitudin- 
ally  and  transversely  disposed  plain 
muscle-fibers.  The  cystic  duct,  the 
couwion  bile-duct,'^  and  the  gall-blad- 
der exhibit  the  same  structure  ;  their 
tunica  propria  is  elevated  in  anasto- 
mosing folds,  the  rugae  ;  here  there 
is  also  a  thin  continuous  layer  of  in- 
terlacing smooth  muscle-fibers.  The 
cylinder  epithelial  cells  of  the  gall- 
bladder are  distinguished  by  their 
height  (0.05  mm.)  from  those  of  the 
common  bile-duct  (0.024  mm.).t  The 
branches  arising  from  the  further  di- 
vision of  the  hepatic  duct,  the  inter- 
lobidar  bile-ducts,  with  decrease  in 
caliber  exhibit  diminishing  thickness  of 
the  wall  ;  the  larger  consist  of  simple 

cylinder  epithelium  and  fibro-elastic  tissue,  the  smallest  possess  only  a 
structureless  membrana  propria  and  a  simple  layer  of  low  epithelial  cells 
provided  with  a  cuticular  border,  which  as  they  approach  the  lobule  annex 
themselves  directly  to  the  trabecul^e  of  liver  cells. | 


Interlobular  vein.      Hepatic  duct. 

Fig.  216. — Scheme  or  an  Hepatic  Lobule,  repre- 
sented in  transverse  section  below  and  in  lon- 
gitudinal section  above.  In  the  left  half  the 
blood-vessels  are  drawn,  in  the  right  half  only 
the  cords  of  hepatic  cells.     X  20. 


*  The  opening  of  the  common  bile-duct  is  encircled  by  smooth  muscle-fibers,  that  are 
partially  connected  with  the  musculature  of  the  intestine ;  they  may  be  designated  a  sphincter. 
Similar  sphincters  occur  at  the  opening  of  the  two  excretory  ducts  of  the  pancreas. 

f  The  vasa  aberrantia  are  blind-ending  bile-ducts  running  outside  of  the  parenchyma  of 
the  liver.  They  are  chiefly  found  at  the  left  border  of  the  liver  (lig.  triangul.  sinistr.),  at  the 
portal  fissure,  and  in  the  vicinity  of  the  vena  cava.  They  represent  the  last  remnants  of  liver 
substance  occurring  at  these  places  in  embryonal  life. 

i  This  transition  is  very  difficult  to  see  and  can  be  distinctly  perceived  only  in  sections  in 
which  the  bile-ducts  have  been  injected  or  have  been  blackened  by  Golgi's  silver  method. 


2.88  HISTOLOGY. 

The  lobules  of  the  Hver  (hepatic  lobules,  liver  islands,  also  erro- 
neously named  acini)  can  be  seen  with  the  unaided  eye,  on  examining 
the  outer  surface  or  a  cut  surface  of  the  organ,  as  irregular  polygonal 
fields,  that  sometimes  are  distinct,  as  in  the  hog,  sometimes  ill-defined, 
as  in  man  and  the  majority  of  mammals.  Their  true  form  is  somewhat  like 
that  of  a  prism  rounded  above,  transversely  blunted  below ;  they  have  a 
height  of  2  mm,  and  a  breadth  of  i  mm.  (Fig.  216).  Close  under  the 
exterior  of  the  liver  the  lobules  often  are  arranged  with  their  apex  look- 
ing toward  the  surface  and  a  section  made  parallel  to  the  surface  will 
pass  through  the  lobules  transversely  {cf.  Fig.  217) ;  but  in  the  interior 

•  '        '    '  Branch  of  portal  vein. 

I       ^  Large  interlobular  bile-duct. 

■  ',         y  /  r        '     --■■^-       ^  Interlobular  connective 

"       ,'  I  y^  ^ ' "  tissue. 


Central  vein. 


\                                              ''       '     - 
\  '  '  -  .      -     _< — ,-... Central  vein. 


Fig.  217. — From  a  Horizontal  Section  of  the  Human  Liver.  X  40-  Three  central  veins,  cut  transversely, 
represent  each  a  center  of  as  many  hepatic  lobules,  that  at  the  periphery  are  but  slightly  defined  from  their 
neighbors.  Below  and  to  the  right  of  the  section  the  lobules  are  cut  obliquely  and  their  boundaries  cannot 
be  distinguished.     Technic  No.  123. 

of  the  liver  the  lobules  stand  in  various  directions.  Each  lobule  con- 
sists of  hepatic  trabeculse  and  blood-vessels  and  is  separated  from  its 
neighbors  by  the  interlobular  connective  tissue,*  which  supports  the 
branches  of  the  excretory  duct  (the  hepatic  duct),  the  branches  of  the 
portal  vein  and  the  hepatic  artery,  of  the  lymph-vessels  and  the  nerves. 
On  examining  a  cross-section  of  a  lobule  of  the  liver  with  low 
magnification,  the  trabeculae  of  hepatic  cells  may  be  recognized  as  cords 
and  small  lamellae  that  extend  from  a  little  vein,  the  central  vein,  situ- 
ated in  the  axis  of  the  lobule,  radially  toward  the  periphery,  and  by 
means  of  lateral  branches  connect  with  neighbor  trabeculae  (Fig.  216  and 
Fig.  217).  By  the  usual  methods  the  gland  lumina  in  these  trabeculae 
cannot  be  seen  ;  only  by  injection  of  the  canal  system  through  the  hepatic 

*  The  sharp  demarcation  of  the  lobules  depends  on  the  quantity  of  the  same. 


THE    DIGESTIVE    ORGANS. 


289 


duct  or  by  the  method  of  Golgi,  which  blackens  the  bile,  can  they  be 
successfully  demonstrated.  It  is  then  evident  that  the  lumen  of  the 
smallest  interlobular  bile-duct  continues  directly  into  the  hepatic  lobule 
and  there  lies  in  the  axis  of  the  hepatic  trabecula.      Longitudinal  section 


True  meshes. 


Lateral  branches  of  bile  capillaries. 


Anastomosis. 


Nucleus  of  the 
wall  of  a 
blood  capil- 
lary. 


Nuclei  of 
hepatic  cells 


kU  '^':S^'^^^h^.M^ 


Blood  capUlaries. 


Portion  of  a  central  vein. 


Fig.  218.— From  a  Cross-section  of  a  Husian  Hepatic  Lobule.  X  300.  The  boundaries  of  the  hepatic 
cells  could  not  be  seen  in  the  preparation.  The  black  dots  are  foreign  matter  due  to  precipitation  of  the  silver. 
Technic  No.  126. 

of  the  lumen  shows  that  it  runs  zigzag  and  is  beset  with  small  lateral 
branches*  (Fig.  2x8),  which,  where  several  trabeculae  of  liver  cells  are  in 


*  These  intercellular  lateral  branches  must  not  be  confused  with  short  lateral  twigs  of  the 
bile  capillaries,  that  terminate  in  a  minute  knob-shape  enlargement.     The  knob  corresponds  to 
a  small  vacuole  occurring  in  the  liver  cell,  which  communicates  with  the  bile  capillary  by  means 
19 


290 


HISTOLOGY. 


Hepatic  cell. 


direct  contact,  by  union  with  other  lateral  branches  may  form  true  meshes  * 
(Fig.  218).  All  the  lumina  lying  in  the  interior  of  the  lobule  are  named 
bile  capillaries.  The  entire  system  of  bile  capillaries  is  freely  united,  not 
only  through  the  meshes,  but  also  through  anastomoses  brought  about 
by  the  union  of  neighbor  hepatic  trabeculae  (Fig.  218)  and  in  thick  sec- 
tions appears  luxuriantly  branched  and  entirely  independent  of  the  tra- 
beculae.      But    thin    sections    show    that   in    the    main    point   the    bile 

capillaries  behave  exactly 
as  other  gland  lumina, 
namely  that  gland  lumen 
(bile  capillary)  and  blood- 
vessel do  not  come  into 
contact,t  but  between  them 
is  intercalated  a  gland-cell 
or  a  portion  of  such  a  cell 
(see  p.  86).  This  is  most 
clearly  recognized  in  thin 
sections  in  which  the  blood 
capillaries  are  cut  trans- 
versely (Fig.  220) ;  in  these 
it  may  also  be  plainly  seen 
that  the  bile  capillaries  run  along  the  surfaces,  the  blood  capillaries  along 


Fig.  220. — Thin  Section  of  the  Liver  of  a  Rabbit,  with  In- 
jected Bile  capillaries.  X  560.  (The  drawing  is  not 
schematic.)  Two  of  the  hepatic  cells  are  in  contact  with  four 
blood  capillaries  (i,  2,  3,  4).  X.  Bile  capUlary  at  the  edge  of 
an  hepatic  cell. 


of  a  delicate  canal  (the  small  lateral  twig).  This  lateral  twig  may  be  regarded  as  an  intracel- 
lular secretory  capillary.  Undoubtedly  these  knobs  are  transient  formations,  only  occurring  in 
connection  with  a  certain  functional  cycle,  are 
drops  of  secretion  that  pass  from  the  hepatic 
cell  into  the  capillary  ;  the  evidence  of  this  I 
detect  herein,  that  entire  sections  of  the  canal- 
icular system  may  be  free  from  knobs,  while  in 
immediate  proximity  each  canaliculus  is  beset 
with  them  (Fig.  219).  It  is  probable  that  the 
formations  resembling  the  secretory  capillaries 
of  the  parietal  cells,  found  in  the  liver  cells  in 
obstruction  of  the  biliary  passages,  belong  to 
the  same  category. 

*  The  number  of  meshes  is  by  no  means 
so  large  as  one  might  infer  from  not  very  thin 
sections  examined  with  low  powers.  Very  frequently  meshes  are  simulated  by  the  very  zigzag 
canaliculi  with  their  lateral  branches  crossing  at  different  planes  (Fig.  221).  One  may  search 
entire  sections,  in  particular  such  as  pass  transversely  through  an  hepatic  lobule,  without  finding 
a  single  true  mesh. 

I  Whether  this  is  invariably  the  case  appears  to  me  latterly  doubtful ;  in  very  thin  in- 
jected sections  of  rabbit's  liver  I  have,  in  isolated  places,  seen  bile  capillaries  close  beside  blood 
capillaries ;  the  same  is  said  to  occur  in  the  dog  and  in  man. 


BUe  capillaries 
without  knobs. 


Bile  capillaries 
with  knobs. 


Fig.  219. — From  A  Section  OF  the  Liver  of  a  Doc. 
X  490.    Technic  No.  126. 


THE    DIGESTIVE    ORGANS. 


>9I 


the  edges  of  the  hepatic  cells  ;  still  this  is  not  an  invariable  rule,  for  bile 
capillaries  are  found  that  also  follow  the  edges  of  the  cells  (Fig.  220,  x), 
a  relation  existing  notably  in  man. 

The  gland-cells  of  the  liver,  the  liver  cells,  hepatic  cells,  are  irregular, 
polyhedral  structures,  which  consist  of  a  granular  protoplasm  and  one 
or  more  nuclei  ;  a  membrane  is  wanting.*  The  protoplasm  contains 
granules  of  pigment  and  glycogen, f  as  well  as  fat  droplets  of  various 


Branch  of  portal 
vein. 


Small  interlobu- 
lar bile-duct, 
continuing  in 
bile  capillaries. 


Large  interlobu- 
lar bile-duct. 


Branch  of  hepat- 
ic artery. 


Bile  capillaries. 


Boundary,  toward  the  central  vein. 

Fig.  221. — Transverse  Section  of  the  Liver  of  a  Dog.     X  240.    Bile  capillaries  blackened  according  to 
the  method  of  Golgi.     Technic  No.  126. 

sizes,  which  latter  are  invariably  found  in  mammalian  animals  and  well- 
nourished  persons.     The  cells  have  a  size  of  from  i8  to  26  11.%     Visible 


*  Where  the  liver  cells  bound  the  bile  capillaries  their  exoplasm  (p.  63)  is  somewhat 
modified  and  is  connected  with  the  cuticular  border  of  the  epithelium  of  the  interlobular  bile- 
ducts  (p.  287).  This  modified  stratum  has  been  inaccurately  described  as  a  special  wall  of  the 
bile  capillary.  With  equal  reason  a  special  wall  other  than  that  formed  by  the  gland-cells 
should  be  ascribed  to  all  gland  lumina. 

I  The  latter  can  be  demonstrated  in  alcohol  preparations  that  have  not  been  treated  with 
aqueous  solutions. 

j  Individual  hepatic  cells  are  distinguished  by  their  greater  diameter,  of  the  body  as  well 
as  of  the  nucleus  ;  such  large  nuclei  divide  in  the  mode  of  amitosis  ;  frequently  one  of  the  two 
nuclei  goes  to  destruction,  in  other  cases  the  nuclei  arising  in  this  way  persist — as  many  as 
seven  have  been  observed. 


292 


HISTOLOGY. 


/ 


15^ 


functional   differences   also  exist  in   the  liver  cells  (Fig.  222  B).     They 
^^^  either  are   small,    dull,   and   indistinctly- 

contoured, — such  conditions  occur  prin- 
cipally in  the  fasting  state, — or  larger, 
clear  in  the  center,  at  the  periphery  pro- 
vided with  a  coarsely  granular  belt — 
appearances  that  occur  chiefly  during 
digestion.  In  man  the  two  states  often 
are  met  in  the  same  liver. 

Of  the  blood-vessels  of  the  liver  the 
portal  vein  assumes  the  role  that  falls  to 
the  artery  in  other  glands,  while  to  the 
hepatic  artery  is  assigned  the  subordi- 
nate task  of  the  maintenance  of  the  interlobular  ramifications  of  the 
bile-duct,  the  portal  vein,  and  the  hepatic  veins. 

From  the  branches  of  the  poi'tal  vein,  called  interlobular  veins,  be- 
cause they  run  between  the  lobules,  spring  numerous  capillaries,  which 


Fig.  222. — Liver  Cells  of  Man.  X  s6o. 
A.  Isolated  liver  cells  containing  smaller 
and  larger  fat-drops,  /  ;  6,  imprint  from 
contact    with    a    blood-vessel.      Technic 

No.    121. 

B.  From  a  section  ;  i,  empty  cells  ;  2,  cells 
filled  with  secretion.    Technic  No.  123. 


Venae  mterlobulares 


Venae  intralobulares  (centrales) 

Vena  mterlobularis 


^J 


Fig.  223. — Horizontal  Section  of  the  Liver  of  a 
Rabbit.  Injected  through  the  portal  vein.  X  40. 
Three  hepatic  lobules  are  represented.  The  in- 
jection mass  filled  only  the  branches  of  the  portal 
vein  (interlobular  veins);  in  the  upper  lobule  it 
penetrated  to  the  central  vein.     Technic  No.  125. 


Fig.  224. — Horizontal  Section  of  the  Liver  of  a 
Cat.  Injected  through  the  vena  cava  inferior. 
X  40.  Four  hepatic  lobules  are  shown.  The 
injection  mass  filled  the  central  veins  and  the  capil- 
laries emptying  into  it,  but  did  not  penetrate  to  the 
interlobular  veins.     Technic  No.  125. 


possess  the  conspicuous  width  of  from  lo  to  \2  p..  They  penetrate 
within  the  lobules,  where  they  lie  between  the  hepatic  trabeculse  (Fig. 
225)  ;   during  their  course  they  repeatedly  anastomose  with  one  another 


THE    DIGESTIVE    ORGANS. 


293 


and  finally  empty  in  a  small  vein  lying  in  the  axis  of  the  lobule,  the  cen- 
tral vein,  or  intralobular  %'cin,  the  transverse  and  longitudinal  section  of 
which  is  visible  even  in  sections 
of  the  uninjected  liver  (Fig.  217). 
The  central  veins  represent  the 
radicles  of  the  hepatic  veins  and 
empty  into  the  snblobiilar  veins, 
which  run  along  the  one  slightly 
flattened  side,  the  so-called  base, 
of  the  hepatic  lobule  (Fig.  226). 
The  branches  of  the  hepatic 
artery  follow  those  of  the  portal 
vein  and  ramify  only  in  the  in- 
terlobular tissue,  where  they 
form  capillary  networks  about 
the  larger  bile-ducts  and  the 
branches  of  the  portal  and  hepa- 
tic veins.  The  veins  proceeding 
from  the  artery  or  its  capillaries 
open  into  the  portal  interlobular 

veins  or  into  the  beginnings  of  the  portal  capillaries.  In  the  capsule  of 
the  liver  (see  below)  the  hepatic  artery  forms  a  wide-meshed  capillary 
plexus. 


Blood  capillaries. 


Bile  capillaries. 


Hepatic  cells. 


Fig.  225. — From  a  Section  of  the  Liver  of  a  Rabbit. 
X  240.  The  portal  capillaries  were  injected  with  a 
red  mass,  the  bile  capillaries  with  a  blue  mass.  The 
hepatic  cells  are  in  contact  with  blood  capillaries  on 
both  sides.  At  a  few  points  the  red  mass  has  retract- 
ed and  given  rise  to  a  space  (/)>  between  the  hepatic 
cells  and  the  portal  capillaries.  The  dark  spots  on 
the  portal  capillaries  are  optical  cross-sections  of 
blood  capillaries  which  run  vertically  through  the 
thickness  of  the  section. 


Hepatic  lobules. 


Interlobular  connective 
tissue. 


Central  (intralobular) 
veins. 


Sublobular  vein. 


Fig.  226. — From  a  Vertical  Section  of  the  Liver  of  a  Cat.  Injected  through  the  vena  cava  inferior.  A 
sublobular  vein  cut  longitudinally;  it  takes  up  the  central  veins.  The  greater  part  of  the  injection  mass  has 
fallen  out  of  the  wide  blood-vessels.     X  is-     Technic  No.  125. 


The  course  of  the  blood-vessels  therefore  is  as  follows  :  the  portal 
vein  enters  at  the  transverse  fissure,  repeatedly  divides  into  branches  that 


294 


HISTOLOGY. 


Bile  capillaries. 


steadily  decrease  in  size  and  run  in  the  connective  tissue  between  the  lob- 
ules as  the  interlobular  veins.  From  these  capillaries  arise,  which  pass 
toward  the  axis  of  the  lobule  and  terminate  in  the  central  vein.  Several  of 
the  latter  unite  in  the  formation  of  each  of  the  sublobular  veins,  which  like 
the  larger  hepatic  veins  they  form  by  their  union  run  between  the  lobules. 
The  Hver  is  provided  with  a  capsule  consisting  of  connective  tissue 
and  elastic  fibers  (that  increase  in  old  age),  the  capsula  fibrosa  (Glissoni), 
which  is  especially  well  developed  at  the  transverse  fissure  and  in  the 
form  of  special  sheaths  for  the  different  vessels  *  penetrates  into  the  in- 
terior of  the  liver ;  here  the  connective  tissue  (interlobular  connective 
tissue)  is  usually  found  in  such  small  amount  between  the  lobules  that 
the   boundaries   of  the   latter  are  very  imperfectly  defined   {cf.  Technics 

No.  122  and  No. 
123).  Delicate 
fibers  ("lattice- 
fibers,"  Gitterfas- 
erii)  derived  from 
the  interlobular 
connective  tissue — 
but  no  elastic  ele- 
ment s — penetrate 
into  the  interior  of 
the  lobules ;  they 
form  the  intralobu- 
lar connective  tis- 
sue,t  which  for  the 
most  part  is  ar- 
ranged in  the  form 
of  a  delicate,  chiefly  radially  placed  latticework  {Gitterwerkes)  (Fig,  227). 
The  lymph-vessels  accompany  the  branches  of  the  portal  vein, 
continue  in  perilobular  lymph  spaces  and  enter  the  interior  of  the 
lobule  with  the  portal  capillaries,  where  an  intimate  connection  with  the 
blood  capillaries  (through  normal  openings  occurring  in  the  capillary 
wall)  is  said  to  exist ;  %  also  the  larger  veins,  from  the  sublobular  veins  on, 

*  The  walls  of  the  hepatic  veins  are  firmly  attached  to  the  liver  substance  by  this  con- 
nective tissue  ;  for  this  reason  the  veins  do  not  collapse  when  cut. 

fThe  socalled  stellate  cells  do  not  belong  to  the  connective  tissue,  but  are  epithelial 
elements  of  the  portal  capillaries.  The  stellate  form  is  caused  by  the  peculiar  arrangement  of 
the  protoplasm  around  the  nucleus.      The  stellate  cells  can  be  seen  only  in  gold  preparations. 

X  Such  connection  is  supported  by  the  fact  that  in  injections  of  the  portal  vein  (in  the 
rabbit)  the  lymph-vessels  become  visible  ;  indeed  the  trophospongium  (p.  64)  of  the  hepatic 
cells  has  been  successfully  injected  through  the  portal  vein,  which  doubtless  could  happen  only 
in  an  indirect  way,  through  the  simultaneous  injection  of  the  lymph-vessels. 


This  much  of  the 
lobule  is  sketched. 

Fig.  227. — From  a  Section  or  Human  Liver.     X  214.     Technic  No.  126. 


THE    DIGESTIVE    ORGANS. 


295 


are  accompanied  by  lymph-vessels.  These  deep  lymph-vessels  are  freely 
connected  with  a  narrow-meshed  network  of  lymph-vessels  occurring 
in  the  capsule  of  the  liver. 

The  nerves  chiefly  consist  ot  nonmedullated  nerve-fibers,  with  which 
only  a  few  medullated  nerve-fibers  are  mingled  ;  they  supply  the  capsule 
of  the  liver  and  enter  the  interior  of  the  organ  with  the  hepatic  vessels, 
the  ramifications  of  which  they  follow  ;  according  to  investigations  on 
mammalian  animals  they  terminate  for  the  greater  part  on  the  hepatic 
vessels,  accompanying  them  into  the  interior  of  the  lobules  ;  a  lesser  por- 
tion end  as  sensory  fibers  in  the  interlobular  tissue  and  as  secretory  fibers 
between  the  liver  cells  (this  has  been  observed  in  the  dove).  Ganglion 
cells  occur  only  in  the  course  of  the  nerves  in  the  wall  of  the  gall-bladder. 

The  secretion  of  the  liver,  the  bile,  frequently  contains  drops  of  fat, 
also  granular  masses  of  bile  pigment.  Cylinder  cells  from  the  bile-ducts 
are  to  be  regarded  as  incidental  admixtures. 


EpitheMal  cells. 


Nuclei  of  connective- 
tissue  cells. 


Fig.  228. — From  the  Greater  Omentum  of  a  Rabbit.  X  240.  The  meshes  are  formed  by  thick  and  thin 
btmdles  of  connective  tissue.  The  wavy  striation  of  the  bundles  can  only  be  indistinctly  seen,  because  the 
preparation  is  mounted  in  xylol  balsam.  At  X  the  epithehal  cells  of  the  opposite  surface  can  be  seen  shim- 
mering through.     Technic  No.  127. 


The  Peritoneum. 
The  peritoneum  principally  consists  of  connective  tissue  bundles 
and  of  numerous  elastic  fiber-nets  ;  the  free  surface  of  the  peritoneum  is 
covered  with  a  simple  layer  of  flat,  polygonal  epithelial  cells  ;  these  cells 
consist  of  superficial  divisions,  very  thin  plates  (in  the  dog  and  the  rab- 
bit they  are  covered  with  a  delicate  hair  border),  the  contiguous  edges  of 
which  are  very  accurately  approximated  (Fig.  228),  and  of  deep  divisions 
enclosing  the  nucleus,  that  are  connected  with  one  another  by  delicate 
processes.      The   size  of  the  plates  varies  according  to  the  stretching  to 


296  HISTOLOGY. 

which  they  are  subjected.  The  connection  with  the  subjacent  parts  (the 
parietes,  the  viscera,  etc.)  is  effected  by  loose  (subserous)  connective 
tissue. 

The  connective-tissue  bundles  are  arranged  in  thinner  (in  the  visceral 
peritoneum)  or  thicker  (in  the  parietal  peritoneum,  in  the  mesentery) 
layers,  chiefly  parallel  to  the  surface,  and  interlace  in  various  directions  ; 
in  certain  localities  (in  the  greater  omentum,  in  the  middle  of  the  lesser 
omentum)  the  bundles  form  a  beautiful  network  with  polygonal  or  rec- 
tangular meshes.  The  strands  of  the  network  also  are  covered  with  flat 
epithelial  cells  (Fig.  228). 

The  number  of  connective-tissue  cells  among  the  bundles  is  on  the 
whole  not  large  ;  only  in  young  animals  are  larger  groups  of  cells  found  ; 
they  resemble  plasma-cells  and  probably  all  stand  in  close  relation  to  the 
formation  of  vessels  {cf.  pp.  94,  135). 

The  elastic  fibers  in  the  deeper  layers  of  the  peritoneum,  particularly 
in  the  parietal  lamella,  are  profuse  and  vigorously  developed. 

The  subserous  tissue  consists  of  loose  connective  tissue,  many  elastic 
fibers,  and  fat,  varying  greatly  in  quantity  ;  it  is  plentiful  where  the  peri- 
toneum is  easily  shifted  over  the  underlying  parts,  but  on  the  liver  and 
the  intestine  so  reduced  that  it  cannot  be  demonstrated  as  a  special  layer. 
At  certain  places,  e.  g.,  in  the  broad  ligaments,  numerous  strands  of 
smooth  muscle-fibers  are  found. 

Blood-vessels  and  nerves  are  scantily  represented  ;  the  latter  partly 
terminate  in  lamellar  corpuscles  {cf.  p.  222). 

Lymph-vessels  occur  in  the  superficial  and  deep  layers  of  the  peri- 
toneum {cf.  p.  141). 

TECHNIC. 

No.  96. — Isolated  squamous  cells  from  the  oral  cavity. — With  a  scalpel 
gently  scrape  the  upper  surface  of  the  tongue  and  mix  the  scrapings  on 
a  slide  with  a  drop  of  salt  solution  ;  apply  a  cover-glass  ;  in  addition  to 
isolated,  pale,  squamous  epithelial  cells  (Fig.  15,  p.  75),  leucocytes  ("sali- 
vary corpuscles  ")  may  be  found,  also,  with  more  vigorous  scraping,  the 
tips  of  filiform  papillae,  which  not  infrequently  are  surrounded  by  finely 
granular,  dark  masses  of  micrococci,  to  which  tufts  of  leptothrix  buccalis 
are  attached.  The  preparation  maybe  stained  under  the  cover -glass  (p. 
53)  with  picrocarmine  and  then  treated  with  dilute  acidulated  glycerol, 
provided  too  many  air  bubbles  do  not  make  the  preservation  of  the  prep- 
aration impossible. 

No.  97. — Mucous  glands  of  the  lips. — These  are  millet-sized  nod- 
ules perceptible  to  touch  and  accessible  for  macroscopic  preparations. 
For  microscopic  preparations  cut  from  the  mucous  membrane  of  a  human 
lower  lip  (not  the  margin  of  the  lip)  i  cm.  cubes  ;  fix  them  in  50  c.c.  of 


THE    DIGESTIVE    ORGANS.  297 

potassium-bichromate -acetic  acid  (p.  32)  and  in  twenty-four  hours  harden 
in  50  c.c.  of  gradually  strengthened  alcohols  (p.  35).  Cut  many  sections, 
not  too  thin,  and  stain  them  with  Hansen's  hematoxylin  (p.  38) ;  place 
the  sections  in  water  and  with  the  naked  eye  select  those  which  include 
the  excretory  duct  and  preserve  them  in  xylol-balsam  (p.  50)  ;  examine 
with  a  low  power  (Fig.  160). 

No.  98. — Dried  gi'OJind  tootli. — For  the  preparation  of  dried  ground 
sections  of  teeth  the  latter  should  be  obtained  immediately  after  they  are 
extracted,  sawed  into  transverse  disks  2  mm.  thick,  glued  with  sealing- 
wax  upon  cork  and  treated  like  No.  61  (p.  177).  If  longitudinal  sections 
are  desired  the  entire  tooth  should  be  glued  to  the  cork.  Longitudinal 
sections  are  to  be  preferred,  since  they  show  all  parts  of  the  tooth  in  a 
i-/;/^/<f  preparation  (Figures  170,  171,  172). 

If  it  is  desired  to  decalcify  the  teeth  of  an  adult,  proceed  as  with 
No.  6^  (p.  178).  The  enamel  consisting  of  earthy  salts  and  only  from  3 
to  5  per  cent,  of  organic  substances  dissolves  completely,  hence  only  the 
dentine  and  cement  remain. 

No.  99. — Odontoblasts. — Remove  the  teeth  from  the  jaws  ot  a  new- 
born child  ;  place  them  in  60  c.c.  of  Miiller's  fluid  ;  after  six  days  the 
pulp  can  be  easily  withdrawn  in  toto  by  means  of  forceps.  With  the 
scissors  cut  from  the  surface  of  the  pulp  a  piece  the  size  of  a  lentil  and 
tease  a  little  the  tolerably  tenacious  tissue  in  a  drop  of  Miiller's  fluid  ; 
apply  a  cover-glass,  press  lightly  upon  it,  and  examine  with  the  high 
power.  At  the  edges  of  the  preparation  the  long  processes  of  the 
odontoblasts  standing  out  like  hairs  will  be  .seen  ;  also  scattered,  com- 
pletely isolated  odontoblasts  (Fig.  175).  In  order  to  preserve,  treat 
under  the  cover-glass  with  distilled  water  for  two  minutes,  tlien  with 
picrocarmine  (p.  53);  when  the  staining  is  completed,  add  dilute  acidu- 
lated glycerol. 

No.  TOO. — Enamel  prisms. — These  are  obtained  by  teasing  frag- 
ments from  the  surface  of  the  lateral  parts  of  the  teeth  of  No.  99  in  a 
drop  of  Mijller's  fluid.  Examine  with  a  high  power.  The  enamel 
prisms  will  be  found  in  groups  of  three  or  more  ;  they  are  distinguished 
by  their  dark  outlines  and  (usually  indistinct)  cross-striation  (Fig.  173). 
Mount  in  glycerol. 

The  prismatic  form  of  the  enamel  prisms  can  be  seen  in  thin  sections 
cut  parallel  to  the  upper  surface  of  the  tooth.  Only  portions  of  a  sec- 
tion exhibit  regular  hexagonal  prisms,  that  is,  only  true  cross-sections 
of  the  prisms  are  hexagonal  (Fig.  174).  The  enamel  of  young  teeth 
may  be  sectioned  without  previous  decalcification. 

No.  loi. — Development  of  teeth. — For  the  study  of  the  early  stages 
select  pig  and  sheep  embryos  ;  these  are  the  most  easily  obtained  at  the 
slaughter  houses  {cf.  No.  67,  p.  180) ;  for  the  first  stage  (Fig.  177)  the  pig 
embryos  should  have  a  size  of  about  6  cm.,*  for  the  second  stage  a  size  of 

*  Measured  from  the  tip  of  the  snout  to  the  root  of  the  tail. 


298  HISTOLOGY. 

about  10  or  11  cm.  For  later  stages  (Fig.  181)  the  inferior  maxilla  of 
newborn  dogs  or  cats  is  very  suitable.  Place  the  heads  (or  the  lower 
jaws)  in  100  c.c.  of  potassium-bichromate-acetic  acid  *  (p.  32)  and  harden 
in  from  80  to  120  c.c.  of  gradually  strengthened  alcohols  (p.  35).  After 
the  heads  have  lain  six  or  eight  days  in  90  per  cent,  alcohol,  they  are  to 
be  decalcified  in  100  c.c.  of  distilled  water  plus  i  or  2  c.c.  of  nitric  acid 
(p.  36).  When  the  decalcification  is  completed,  in  from  three  to  eight 
days,  harden  again  in  alcohol.  In  five  or  six  days  cut  off  the  lower  jaw 
and  divide  it  in  front  in  the  middle  (larger  jaws  should  be  cut  vertically 
into  pieces  i  or  2  cm.  long)  ;  stain  the  pieces  in  bulk  in  borax-carmine.f 
When  the  staining  and  decolorization  are  completed  the  tissue  is  to  be 
transferred  to  absolute  alcohol,  in  which  it  must  remain  for  several  days  ; 
it  is  then  embedded  in  liver  and  sectioned.  It  is  necessary  to  cut  many 
(20  to  40)  thick  sections,  since  only  those  which  pass  through  the  middle 
of  the  tooth,  or  its  anlage,  can  be  used.  Mount  in  xylol-balsam.  Not 
infrequently  in  sectioning  the  enamel  organ  is  lifted  from  the  papilla,  so 
that  a  free  space  exists  between  the  two.  The  dentine  is  often  stained  in 
different  tones  of  red  ;  this  is  due  to  the  different  ages  of  the  calcified 
and  uncalcified  strata  of  the  dentine. 

No.  102. — PapillcB  filifornies,  fungiformes,  vallatce ;  folliculi  lin- 
guales. — Cut  pieces  2  cm.  square  from  the  mucous  membrane  of  the 
tipper  surface  of  a  human  tongue.  Each  piece  should  have  some  of  the 
muscle  tissue  attached  to  its  lower  surface  ;  for  fungiform  papillae  cut  the 
piece  from  the  tip  of  the  tongue  ;  for  filiform,  from  the  middle  of  the 
tongue  ;  for  vallate,  from  the  root  of  the  tongue  and  for  lingual  tonsils, 
the  punctiform  openings  of  which  can  be  seen  with  the  naked  eye,  from 
the  root  of  the  tongue,  and  place  them  in  100  or  200  c.c.  of  Miiller's 
fluid  (p.  33).  The  fluid  must  be  changed  several  times;  after  two  weeks 
wash  the  tissue  and  harden  it  in  50  c.c.  of  gradually  strengthened  alco- 
hols (p.  35).  For  filiform  papillae  cut  thick  sagittal  sections  of  the 
tongue  and  do  not  stain  them  ;  stain  the  other  sections  in  Hansen's 
hematoxylin  (p.  38)  and  mount  in  xylol-balsam  (Figs.  183,  184,  185). 
For  the  preparations  represented  in  Fig.  161  and  Fig.  186  the  tissue  was 
fixed  and  hardened  in  55  c.c.  of  absolute  alcohol.  Rabbits'  tongues  may 
be  placed  in  toto  in  200  c.c.  of  Miiller's  fluid  ;  the  subsequent  treatment 
is  the  same.  Thick  cross-sections  through  the  anterior  half  of  the  entire 
tongue  are  suitable  for  the  study  of  the  arrangement  of  the  lingual 
muscles.  Thin  sections  of  the  root  of  the  tongue  show  beautiful  mucous 
and  also  serous  glands. 

No.  103. — TJie  tonsils. — The  tonsils  of  adult  man  do  not  furnish 
instructive  preparations.      They  should  be  treated  according  to  technic 

*  Objects  fixed  in  Miiller's  or  in  Zenker's  fluid   are  also  useful. 

t  Bulk  staining,  despite  the  length  of  the  procedure,  is  preferable  to  individual  staining 
of  sections  with  hematoxylin,  because  too  many  sections  must  be  stained  which  on  investi- 
gation are  found  to  be  useless. 


THE    DIGESTIVE    ORGANS.  299 

No.  102.     The  tonsils  of  the  rabbit  and  the  cat  are  recommended  ;  to 
find  them  proceed  as  follows  : 

Dissect  the  skin  from  the  anterior  surface  of  the  throat  and 
with  a  pair  of  stout  scissors  cut  through  the  trachea  and  esophagus 
above  the  sternum,  grasp  the  cut  end  of  the  trachea  with  forceps 
and  with  the  scissors  dissect  out  both  tubes  up  to  the  head  of  the 
esophagus,  keeping  close  to  the  anterior  surface  of  the  vertebral 
column ;  at  the  same  time  the  cornua  of  the  hyoid  bone  will  be 
divided.  Here  the  wall  of  the  pharynx  is  to  be  divided  ;  then  cut 
through  the  musculature  close  to  the  median  edges  of  the  inferior 
maxilla  up  to  the  angle,  also  through  the  hgaments  of  the  tongue.  (In 
the  rabbit  it  is  advisable  to  divide  both  angles  of  the  mouth  and  with 
scissors  introduced  within  the  mouth  cleft  to  sever  the  ligaments  and 
the  genioglossus  muscle).  Draw  the  trachea  and  attached  structures 
downward,  press  the  tongue  down  between  the  rami  of  the  inferior 
maxilla  and  divide  its  remaining  attachments  (to  the  palate)  close  to  the 
bone.  Put  the  tongue  down  with  its  free  surface  looking  upward  ; 
with  delicate  scissors  divide  the  posterior,  wall  of  the  pharynx  in  the 
median  line  down  to  the  larynx  and  pull  the  walls  apart;  the  ton- 
sils will  then  be  seen  as  a  pair  of  oval  prominences,  about  5  mm. 
long,  on  the  lateral  walls  of  the  pharynx.  They  may  be  fixed  in  60 
c.c.  of  potassium-bichromate-acetic  acid  (p.  32),  hardened  in  50  c.c.  of 
gradually  strengthened  alcohols  (p.  35),  stained  with  Hansen's  hema- 
toxylin (p.  38)  or  with  hematoxylin  and  eosin  (p.  39),  and  mounted  in 
xylol-balsam. 

No.  104. — TJic  esophagus. — Pieces  from  2  to  6  cm.  long  of  the 
entire  tube  are  to  be  fixed  in  60  c.c.  of  Miiller's  fluid  (p.  33)  and  in  two 
weeks  hardened  in  50  c.c.  of  gradually  strengthened  alcohols  (p.  35)  ; 
stain  with  Hansen's  hematoxyhn  (p.  38) ;  mount  in  xylol-balsam  (Fig. 
188). 

No,  105. —  The  ineinbya)ies  of  the  stomach. — For  topographic  prep- 
arations place  pieces  from  2  to  5  cm.  square  for  six  hours  in  100 
c.c.  of  3  per  cent,  nitric  acid  (p.  32).  Detach  the  gastric  contents  ad- 
hering to  the  mucous  membrane  by  moving  it  slowly  to  and  fro  in  the 
acid.  In  a  half  hour  renew  the  acid  ;  harden  in  60  c.c.  of  gradually 
strengthened  alcohols  (p.  35).  Mount  thick  unstained  sections  and  thin 
sections  stained  with  Hansen's  hematoxylin  (p.  39)  and  with  eosin  in 
xylol-balsam  (Fig,  190). 

No.  106. — Fresh  gastric  glands. — From  the  fundus  of  the  stomach 
of  a  rabbit  just  killed  cut  pieces  about  2  cm.  square  and  separate  the 
loosely  attached  muscular  coat  from  the  mucous  membrane.  Grasp  the 
latter  with  forceps  at  the  left  edge  and  with  fine  scissors  cut  a  very 
thin  strip,  from  0.5  to  i  mm.  broad  ;  tease  it  well  in  a  drop  of  0.5  per 
cent,  salt  solution.  The  body  and  fundus  of  the  glands  can  be  sat- 
isfactorily isolated  without  much  trouble.  The  protoplasm  of  the  parietal 


lOO  HISTOLOGY. 


cells   can   be   distinctly  seen  (Fig.  229  B),   the   chief  cells  are  invisible. 

The  nuclei  may  be  stained  with  picrocarmine  (p.  53)  and  the  preparation 

mounted  in  dilute  glycerol.     The  isolation  of  the 

/  pylorus  glands  can  be  accomplished  only  by  very 

i~"^^-B  careful  teasine. 


fe-»u^ 


No.  107. — Isolated  gastric  epithelium. — Place 
;;>ferfft  a  piece  i  cm.  square  of  gastric  mucous  membrane 

WMf^  fQj.  about  five  hours  in  30  c.c.  of  Ranvier's  alcohol 

(see  further  p.  29).     In  the  majority  of  the  cells  the 
mucous  portion  occupies  a  large  division  and  they 
have  the  appearance  of  those  pictured  in  Fig.  25  <:, 
^     ;:-::;  p.  80.     The  preparation  may  be  stained  under  the 

I  cover-glass  with  picrocarmine  and  mounted  in  di- 

luted acidulated  glycerol  (p.  53). 

%uy:0  No.  108. — Gastric  glands. — The  stomach  of  a 

cat  or  dog  that  has  been  fasting  for  one  or  two  days 

Fig.  229. — Lower  Half  of        .  .    , ,  ,      ,      r^,         .  i       r  i.1.  u 

AN  Isolated  Fundus-      IS  especially  recommended,    i  he  stomach  ot  tne  rab- 
x'*2^.  °i,  ParietafceU;      bit,   ou  account  of  the  very  small  size  of  the  chief 
if,  membrana  propria.  '      ^gjjg^  jg  j^^g  suitable.    Disscct  off  the  mucous  mem- 
brane from  the  muscular  coat  and  place  pieces  of  the 
former  about  i  cm.  square  in  10  c.c.  of  absolute  alcohol.    In  about  a  half 
hour  transfer  them  to  20  c.c.  of  fresh  alcohol.       ThQform  of  the  glands 
can  be  recognized  in  moderately  thin  sections  ;  the  only  difficulty  is  the 
circumstance  that  the  gland-sacks  stand  very  close  together.     The  be- 
ginner may  not  recognize  the  glands  and  may  mistake  for  them  the  gas- 
tric pits  lined  with  clear  epithelium.      The  stomach  of  man,  which  how- 
ever is  suitable  for  use  only  for  a  few  hours  after  death,  exhibits  this 
disadvantage  in  a  lesser  degree.      For  the  study  of  the  minute  structure 
of  the  glands  and  of  the  surface  epithelium  embed  the  tissue  in  hver  and 
cut  the  thinnest  possible  sections. 

{a)  For  fundus  glands,  chief  a7id  parietal  cells,  cut  vertical  or,  better, 
horizontal  sections  of  the  mucous  membrane  and  stain  them  with  Han- 
sen's hematoxylin  for  two  or  four  minutes.  Wash  the  sections  thor- 
oughly in  30  c.c.  of  distilled  water,  which  must  be  changed  as  often  as 
it  becomes  bluish — about  once  or  twice.  Transfer  them  to  5  c.c.  of  a 
0.03  per  cent,  solution  of  Congo  red  (p.  25),  for  from  three  to  six 
minutes,  wash  two  minutes  in  distilled  water  and  mount  in  xylol-balsam. 
If  the  sections  are  too  thick  everything  appears  red  ;  the  large  red 
parietal  cells  cover  the  smaller  chief  cells  ;  examine  the  thinnest  parts  of 
the  section,  especially  the  fundus  of  the  glands,  where  the  parietal  cells 
are  not  so  exceedingly  profuse.  The  parietal  cells  can  be  recognized 
with  the  low  power  as  isolated  red  spots  on  a  rose-red  ground.  With 
the  high  power  the  pale  blue  smaller  chief  cells  can  be  seen.  The  very 
narrow  lumen  of  the  fundus  glands  can  be  best  seen  in  cross-sections 
(sections  parallel  to  the  surface  of  the  mucosa).  The  lateral  twigs  of  the 
chief  lumen  can  only  be  perceived  in  very  choice  sections  (Fig.  192). 
Figure  191  is  a  combination  of  several  thin  longitudinal  sections. 


THE    DIGESTIVE    ORGANS.  3OI 

(b)  For  pylorus  glands  stain  vertical  and  horizontal  sections  of  the 
mucosa  with  Hansen's  hematoxylin  and  mount  in  xylol-balsam.  The 
lumen  of  the  pylorus  glands  is  wider  (Fig.  194).  Owing  to  the  extreme 
sinuosity  of  the  glands,  thin  sections  contain  but  few  glands  cut  in  their 
entire  length,  mostly  only  parts  of  glands. 

No.  109. — Duodenal  glands. — Cut  open  lengthwise  the  stomach  and 
duodenum  of  a  cat,  remove  the  contents  by  swaying  gently  to  and  fro 
in  salt  solution  (p.  20),  and  fasten  the  pyloric  end  of  the  stomach  and 
the  upper  half  of  the  duodenum,  in  all  a  piece  5  or  6  cm.  long,  to  a 
cork  plate  by  means  of  quills.  Place  the  whole  for  six  hours  in  100  c.c. 
of  3  per  cent,  nitric  acid  with  the  tissue  side  downward.  Further  treat- 
ment like  No.  III.  Cut  longitudinal  sections,  which  simultaneously 
pass  through  pylorus  and  duodenum.  Stain  with  Hansen's  hematoxy- 
lin. Mount  in  xylol-balsam.  The  preparations  represented  in  figures 
200  and  201  were  fixed  after  technic  No.  120. 

No.    1 10. — EpitJielimn  and  villi  of  the  small  intestine. — From  the 

middle    portion  of   the    small    intestine  of    a  rabbit   just    killed    cut  a 

piece  one  cm.  long,  open  it  along  its  length  and  remove  the  contents  by 

^-^^-r^  ^  carefully  pouring  over  it  0.7  per  cent,  salt  solution. 

^\^        f  Then  grasp  the  piece  at  the  left  edge  with  the  forceps, 

1  with  fine  scissors  cut  off  a  small  strip  and  spread  it 

~^,         out  in  a  drop  of  salt  solution  on  a  slide  placed  on 

a  black  background.      With  the  unaided  eye  one  can 

;  ^  see  the  villi  projecting  from  the  edge  of  the  prepara- 

^       -     1^,^  ^"^o"-      Examine  the  preparation  ■zcvV/z^w/' a  cover-glass, 

"'"^^^i^.l  with  the  low  power.      The  villi  will  be  seen  partly  ex- 

FiG.    230.— Intestinal     tended,  partly  Contracted  ;  the  latter  condition  may  be 

mT^"x°o. '^  ^^^      recognized  by  transverse  folds  running  across  the  villus 

(Fig.    230).      Details  cannot   be   detected.      Apply   a 

cover-glass  ;  the  villi  become  flattened  and  appear  clearer  ;  the  cylindrical 

epithelium  and  close  beneath  this  the  loops  of  the  capillary  blood-vessels 

can   be  distinctly  seen.      If  the  epithelium   contains   goblet-cells,  these 

appear  as  bright,  shining,  rounded   spots.      For  the  investigation  of  the 

epithelium  proceed  as  follows  : 

{ci)  Tease  the  piece  a  little  ;  in  this  way  cylinder  cells,  singly  and  in 
groups,  are  loosened,  which  are  to  be  examined  with  the  high  power. 
Not  infrequently  some  cylinder  cells  are  found  inflated  to  a  spherical 
form.  The  cuticular  border  is  sometimes  separated  in  very  distinct  rods. 
Goblet-cells  when  present  may  be  recognized  by  their  homogeneous 
appearance  and  if  carefully  focused  the  sharply  outlined  orifice  may  be 
perceived.  Occasionally  the  epithelial  cells  are  difficult  to  loosen  from 
the  basement  membrane  ;  in  such  cases  make  a  second  investigation  an 
hour  later,  when  the  epithelium  will  be  sufficiently  macerated  to  be 
brushed  off. 

{J})  For  permanent  preparations  place  pieces  i  cm.  square  of  the 
intestine  opened  lengthwise  in  30  c.c.  of  Miiller's  fluid.  In  three  or  five 
days  take  the  tissue  out,  scrape  it  with  the  tip  of  a  scalpel,  and  distribute  a 


302  HISTOLOGY. 

little  of  the  scraping  in  a  drop  of  diluted  glycerol ;  cover-glass  ;  high 
power  (Fig.  198  A). 

No.  III. — Sections  of  the  S7nall  intestine. — Place  pieces  from  2  to 
4  cm,  long  of  the  intestine  of  a  rabbit,  better  of  a  puppy  or  a  kitten,  in 
100  or  200  c.c.  of  3  per  cent,  nitric  acid.*  After  six  hours  the  pieces 
are  to  be  hardened  in  100  c.c.  of  gradually  strengthened  alcohols.  Cross- 
sections  can  be  made  through  the  entire  intestinal  tube  ;  in  most  cases 
only  fragments  of  the  villi  are  thus  obtained  ;  to  obtain  entire  villi  cut 
open  with  a  razor  the  hardened  intestine  along  its  length,  pin  it  with 
needles  on  a  cork  plate,  with  the  mucosa  uppermost.  The  villi  can  be  seen 
spreading  apart,  with  the  unaided  eye.  Cut  thick  sections  of  the  mounted 
intestine  and  stain  them  for  one  minute  with  Hansen's  hematoxylin  and 
mount  in  xylol-balsam.  Goblet-cells  are  very  frequently  found  in  the 
epithelium  (Fig.  198  B).  Staining  in  bulk  with  borax-carmine  is  strongly 
advised. 

The  human  intestine  before  being  placed  in  the  nitric  acid  must  be 
cut  open  and  washed  in  the  same  fluid.  It  is  advisable  to  pin  pieces 
about  5  cm.  square  to  a  cork  plate  and  thus  to  place  them  in  the  fixing 
and  hardening  fluids.  If  the  intestine  is  not  absolutely  fresh  the  entire 
superficial  epithehum  loosens,  so  that  the  naked  connective-tissue  villi  are 
exposed. 

Horizontal  sections  of  the  intestine  furnish  very  beautiful  pictures. 
Not  infrequently  the  cross-sections  of  the  glands  drop  out  and  then  only 
the  connective-tissue  tunica  propria  remains.  In  these  preparations  the 
goblet-cells  all  appear  as  clear  bodies  of  equal  size  and  therefore  afford 
no  clue  in  regard  to  the  topography  of  the  secretory  phases  of  the  cell. 

For  the  latter  purpose  the  following  is  recommended : — 

No.  112. — T^dple  staining  of  the  intestine. — Small  pieces  of  tissue 
are  to  be  fixed  in  Flemming's  mixture  (p.  34),  hardened  in  gradually 
strengthened  alcohols,  and   subsequently  treated  according  to   No.  ii, 

P-  43- 

No.  113. — Agminate d  nodules  {patches  of  Peyer). — These  can  be 
seen  shimmering  through  the  uninjured  fresh  intestinal  wall  of  the  rab- 
bit, but  in  the  dog  and  the  cat,  on  account  of  the  thickness  of  the  mus- 
culature, they  are  often  imperceptible.  In  the  latter  animals  patches  are 
constant  at  the  point  where  the  small  intestine  opens  into  the  large.  Cut 
out  the  portion  of  the  intestine  of  a  rabbit  containing  the  Peyer's  patches 
and  proceed  according  to  the  method  given  in  No.  ill.  In  the  cat 
take  the  lowermost  portion  of  the  ileum  (about  2  cm.)  with  a  piece  of 
the  cecum  of  the  same  length ;  slit  them  open  lengthwise  and  span  them 
out  on  a  cork  plate,  with  the  mucosa  uppermost.  Usually  the  mucosa 
is  covered  with  a  tenacious  excrement,  difficult  to  remove  by  washing, 

*  If  the  intestine  is  placed  in  the  reagent  immediately  after  death  the  muscles  of  the  villi 
contract  and  a  separation  of  the  connective  tissue  from  the  epithelium  is  then  the  invariable  result 
[cf.  Figs.  195  and  196).  Therefore  it  is  advised  to  let  the  intestine  grow  cold  before  putting  it 
in  the  fixing  fluid. 


THE    DIGESTIVE    ORGANS.  3O3 

which  glues  the  villi  together,  so  that  only  oblique  sections  of  the  latter 
can  be  obtained.      Further  treatment  like  No.  1 1 1  (Fig.  203). 

Closely  crowded  nodules  are  found  in  the  blind  half  of  the  vermi- 
form process  of  the  rabbit,  which  encroach  upon  the  mucosa  and  com- 
press it  within  such  narrow  areas  that  cross-sections  exhibit  very  compli- 
cated pictures,  scarcely  intelligible  to  the  beginner. 

Fixation  in  o.  i  per  cent,  chromic  acid  (p.  32),  with  hardening  in 
gradually  strengthened  alcohols,  makes  the  germinal  layers  very  distinct, 
but  it  is  not  as  useful  for  the  remaining  elements  as  the  nitric  acid. 

No.  1 14. — The  large  intestine. — Treat  empty  pieces  like  No.  1 1 1  or 
No.  112  [cf.  Fig.  26,  p.  81).  Pieces  filled  with  feces  must  be  cut  open, 
washed,  and  spanned  on  cork  (Fig.  202). 

No.  115. — Fresh  crypts  of  the  large  intestine  of  the  rabbit. — Cut  a 
piece  I  cm.  long  from  the  lowermost  portion  of  the  large  intestine  (be- 
tween two  spherical  masses  of  feces),  place  it  on  a  dry 
slide,  open  it  with  the  scissors,  and  spread  it  out  with 
the  mucous  surface  uppermost ;  add  a  drop  of  0.7  per 
cent,  salt  solution,  grasp  the  piece  with  forceps  at  the 
left  edge  and  with  fine  scissors  cut  off  an  extremely  thin 
strip.  Transfer  this  with  a  drop  of  salt  solution  to  an- 
other slide  ;  by  means  of  needles  separate  the  muscu- 
laris  from  the  mucosa  and  tease  the  latter  a  very  little  ; 
apply  a  cover-glass  with  slight  pressure.  With  a  low 
power  the  crypts  can  be  readily  seen,  but  it  is  difficult 
to  detect  their  orifices  (Fig.  231).  The  epithelial  cells  ^'^f/r^^^u.^x^so!"'"' 
are  often  granular  in  the  portion  bordering  the  lumen. 
With  the  high  power  the  cylinder  epithelium  of  the  surface  can  be  well 
seen,  from  the  side  and  from  the  surface.  The  content  of  the  goblet- 
cells  often  is  not  clear,  as  in  sections,  but  dark  and  granular. 

No.  116. — Blood-vessels  of  the  stomach  and  the  intestines. — A 
stomach  and  intestine  injected  (p.  48)  from  the  descending  aorta  are  to 
be  fixed  in  from  50  to  200  c.c.  of  Miiller's  fluid  and  hardened  in  grad- 
ually strengthened  alcohols.  One  portion  of  each  should  be  cut  into 
thick  (up  to  I  mm.)  sections  and  mounted  unstained  in  xylol-balsam 
(Fig.  205),  and  another  part  used  for  horizontal  preparations,  which  with 
the  low  power  and  change  of  focus  are  very  instructive.  For  this  pur- 
pose pieces  of  the  large  intestine  i  cm.  square  can  be  transferred  from 
absolute  alcohol  to  5  c.c.  of  turpentine,  instead  of  carbol-xylol,  for  vig- 
orous clearing  and  mounted  in  xylol-balsam.  It  is  also  easy  to  strip  the 
muscularis  from  the  mucosa  and  mount  the  separate  membranes  in 
xylol-balsam. 

No.  1 17. — Nerve  plexuses. — For  this  purpose  intestines  with  a  thin 
muscularis  are  preferable,  therefore  the  intestine  of  the  rabbit  and  guinea- 
pig  (not  of  the  cat)  are  especially  suitable.  It  is  not  necessary  that  the 
object  be  absolutely  fresh;  the  small  intestines  of  children  several  days 
after  death   can   still   be    used.      Prepare   200  c.c.  of  a  dilute  solution  of 


304  HISTOLOGY. 

acetic  acid  ( lo  drops  of  glacial  acetic  acid  or  25  drops  of  the  ordinary  acetic 
acid  to  200  c.c.  of  distilled  water).  Then  separate  a  piece  from  10  to  30 
cm.  long  of  the  small  intestine  from  the  mesentery.  Cut  it  off  and  with 
the  finger  lightly  press  out  the  contents ;  tie  one  end  of  the  piece  of  in- 
testine and  fill  it  at  the  other  end  with  the  dilute  acetic  acid  ;  tie  the  open 
end  and  place  the  whole  piece  in  the  remainder  of  the  diluted  acetic  acid. 
In  one  hour  change  the  fluid.  In  twenty-four  hours  transfer  the  intestine 
to  distilled  water,  with  scissors  open  it  along  one  side  of  the  line  of  at- 
tachment of  the  mesentery  and  cut  off  a  piece  i  cm.  long.  The  muscu- 
laris  can  be  readily  separated  from  the  mucosa  with  the  aid  of  forceps  ; 
the  two  membranes  are  only  firmly  united  at  the  attachment  of  the 
mesentery. 

{a)  Plexus  inyenteric2is. — If  a  piece  of  black  paper  be  placed  under 
the  glass  dish  containing  the  tissue  the  white  nodal  points  of  the  plexus 
can  be  seen  by  the  unaided  eye.  Transfer  a  piece  of  the  muscularis, 
about  I  cm.  square,  in  a  drop  of  the  dilute  acetic  acid  to  a  slide;  ex- 
amined with  the  lower  power  it  furnishes  a  very  pretty  picture  (Fig. 
206  A).  If  it  is  desired  to  preserve  the  preparation  place  the  tissue  for 
one  hour  in  30  c.c.  of  distilled  water,  which  must  be  changed  several 
times,  and  then  for  from  eight  to  sixteen  hours  in  5  or  10  c.c.  of  a  i  per 
cent,  osmic  acid  solution,  in  the  dark ;  wash  the  piece  quickly  in  distilled 
water  and  mount  in  diluted  glycerol.  The  osmium  preparations  are  not 
as  beautiful  as  the  fresh  ones  in  the  acetic  acid.  In  the  guinea-pig  both 
strata  of  the  muscularis  can  be  readily  separated  *  (if  the  intestine  is  abso- 
lutely fresh  on  being  filled  with  the  dilute  acid) ;  the  plexus  remains  at- 
tached to  one  stratum.  Pieces  of  this  should  be  placed  for  one  hour  in 
distilled  water,  then  treated  with  gold  chlorid  (p.  47),  and  mounted  in 
xylol-balsam.  The  gold-chlorid  treatment  is  less  adapted  to  human  in- 
testines, since  both  the  muscular  layers  are  also  stained  red  and  partially 
conceal  the  plexus. 

{U)  Plexus  sitbnuicosus. — With  a  scalpel  scrape  the  epithelium  from 
the  isolated  mucosa;  place  a  piece  about  i  cm.  square  on  a  slide;  apply 
a  cover-glass,  press  upon  it  slightly,  and  examine  with  low  powers  (Fig. 
206  E).  To  preserve  the  preparation  proceed  as  in  No.  117  {a);  except 
that  it  is  advisable  to  span  the  pieces  on  cork  and  before  transferring 
them  from  the  ninety-five  per  cent,  alcohol  to  the  carbol-xylol  to  press 
them  somewhat,  in  order  that  the  alcohol  may  be  completely  removed 
from  the  spongy  mucosa. 

In  addition  to  nerves  many  blood-vessels  are  present,  which  are 
easily  recognized  by  the  structure  of  their  walls,  in  part  by  the  trans- 
versely placed  nuclei  of  the  muscle-fibers. 

No.  118. — The  parotid,  submaxillary,  and  snblingjial  glands. — Cut 
from  the  named  glands  (human  glands  in  winter  are  useful  three  or  four 
days  after  death)  a  number  of  pieces  from  0.5  to  i  cm.  square  and  place 

*  Possibly  the  cause  of  the  firm  attachment  of  the  muscle  strata  in  man  lies  in  the  age  of 
the  object. 


THE    DIGESTIVE    ORGANS.  305 

them  in  30  c.c.  of  Zenker's  fluid  *  (for  further  treatment  see  p.  33). 
Stain  one  piece  in  bulk  in  borax-carmine  (p.  40).  Embed  another  un- 
stained piece  in  liv^er  and  cut  the  thinnest  possible  sections ;  small  frag- 
ments* about  2  mm.  long  can  be  used;  stain  them  in  Hansen's  hematoxy- 
lin (p.  38),  two  or  three  minutes;  the  transfer  of  the  sections  to  the 
staining  solution  must  be  done  slowly,  or  the  delicate  structures  will  be 
torn  to  pieces  ;  then  stain  with  eosin  (No.  3  b,  p,  39),  and  mount  in  xylol- 
balsam.  (Very  thin  sections  should  be  examined  in  w^ater  after  the  stain- 
ing in  hematoxylin  is  completed,  since  the  cell  boundaries  are  then  very 
much  more  distinct.)  If  the  staining  is  successful  the  salivary  tubules 
and  the  crescents  are  red.  In  the  sublingual  gland  and  in  the  mucous 
cells  of  the  submaxillary  gland  the  membrana  propria  also  stains  red;  it 
must  not  be  confused  with  the  sections  of  the  crescents,  which  latter  are 
granular,  while  the  membrana  propria  has  a  homogeneous  appearance 
(Fig.  166).  The  mucous  cells  in  the  borax-carmine  preparations  are 
clear  throughout.  In  the  sections  stained  with  hematoxylin  they  are 
sometimes  clear,  sometimes  a  pale  blue  of  different  shades;  the  portion 
which  stains  is  a  reticulum  which  occurs  in  certain  functional  stages  of 
each  mucous  cell.  The  very  short  intercalated  pieces  of  the  submaxil- 
lary gland  are  difficult  to  find  (Fig.  168);  on  the  other  hand,  they  may 
be  easily  seen  in  the  parotid  gland  (also  in  that  of  the  rabbit).  Of  the 
end-pieces  only  those  which  have  been  accurately  halved  are  suitable  for 
study.  The  numerous  oblique  and  tangential  sections  are  often  very 
difficult  to  understand. 

Xo.  1 19.  —  The  Pancreas. — The  human  pancreas  as  a  rule  cannot  be 
used.  The  treatment  is  the  same  as  for  the  parotid  gland,  Technic  No. 
1 18.  By  this  method  the  characteristic  granular  zone 
of  the  gland-cells,  bordering  the  lumen,  can  only  be 
seen  with  high  powers  and  then  not  always,  for  the 
granules  are  exceedingly  sensitive  to  water  and  very 
difficult  to  preserve.  If  a  pin-head  sized  piece  of  the 
fresh  pancreas  of  a  cat  or  other  mammal  is  teased  in 
a  drop  of  0.75  per  cent,  salt  solution  and  examined 
with  a  low  power  the  end-pieces  will  appear  spotted ; 

1  ,  .11  ^1  1  1-    •  Fig.  232.— Gland-cfxls 

the  spots  are  the  partly  clear,  partly  granular  divi-  from  the  pancreas 

sions  of  the  cells.      With  high  powers  the  picture  is  groups  (f/"ceiis°as 

liL-p   'Ficr     o -> ->  they  usually  appear; 

11  JVC   i-  i^-    -J--  below    two    isolated 

No.  1 20. — Granules  of  the  salivary  glands,  the 
pancreas,  and  the  cells  of  Paneth. — Fix  perfectly  fresh  pieces  in  potas- 
sium-bichromate-formol  (p.  33)  and  harden  in  ascending  alcohols  (p.  35). 
Stain  very  thin  sections  with  Heidenhain's  iron-hematoxylin  (p.  44)  or 
with  acid  fuchsin.  In  staining  with  the  latter  add  from  i  to  3  drops  of 
the  solution  to  from  5  to  10  c.c.  of  absolute  alcohol,  and  leave  the  sec- 
tions in  this  diluted  stain  for  24  hours.  In  many  cases  the  granules  can 
be  plainly  distinguished  only  with  an  immersion  lens. 

*The  preparations  represented  in  figures  164,    166,  168   were  fi.xed  and  hardened  after 
technic  No.  loS. 
20 


3o6 


HISTOLOGY. 


No.  12  1. — Liver  cells. — Make  an  incision  in  a  fresh  liver  and  with 
the  blade  of  a  scalpel  obliquely  placed  scrape  the  cut  surface.  Transfer 
the  brown  liver  tissue  adhering  to  the  blade  to  a  slide  and  add  a  drop  of 
salt  solution.  Apply  a  cover-glass.  Examine  first  with  the  low  power, 
then  with  the  high  (Fig.  222  A).  In  addition  to  the  liver  cells  the 
preparation  contains  numerous  colored  and  colorless  blood-cells. 

No.  122. — Hepatic  lobules. — Place  small  pieces  (about  2  cm.  cubes) 
of  a  pig's  liver  in  from  30  to  50  c.c.  of  absolute  alcohol.  The  majority 
of  the  lobules  are  hexagonal  ;  they  can  be  seen  on  the  exterior  of  the  liver 
with  the  unaided  eye  and  after  a  moment  become  distinctly  visible  on  the 
cut  surface.  The  section  of  the  central  vein  also  becomes  visible.  In  about 
three  days  sections  can  be  cut;  stain  them  with  Hansen's  hematoxylin 
(p.  38).  The  division  into  lobules  can  be  well  seen  with  the  low  power, 
but  the  hepatic  cells,  as  well  as  the  bile  ducts,  are  less  satisfactory  for 
study.      Better  for  this  purpose  is  the  following. 

No.  \2i.—Hiunan  liver. '^ — Place  pieces  about  2  cm.  square,  as  fresh 
as  possible,  for  four  weeks  in  200  c.c.  of  Muller's  fluid  for  fixation  and 
then  in  100  c.c.  of  gradually  strengthened  alcohols  for  hardening.  Ex- 
amine unstained  sections,  cut  parallel  and  also  vertical  to  the  surface,  and 
stain  others  with  Hansen's  hematoxylin  or  with  this  and  eosin  (p.  39)  ; 
mount  in  xylol-balsam.  The  demarcation  of  the  lobules  is  indistinct, 
because  of  the  slight  development  of  the  interlobular  connective  tissue. 
The  division  into  lobules  can  be  more  readily  perceived  on  macroscopic 
inspection,  than  on  investigation  with  the  microscope.  For  orientation 
the  beginner  should  recall  that  isolated  sections  of  blood-vessels  always 

represent  intralobular  veins  ;  while  groups 
of  such  sections  represent  branches  of  the 
portal  vein,  the  hepatic  artery,  and  the  bile- 
duct,  and  always  correspond  to  interlobular 
structures.  Exact  transverse  sections  of 
central  veins  can  also  be  recognized  by  the 
trabeculae  of  hepatic  cells  radiating  from 
them  (Fig.  217). 

No.  124. — For  the  demonstration  of 
the  capillaries  and  the  intralobular  connec- 
tive tissue^  which  in  ordinary  preparations  is 
scarcely  visible,  shake  a  number  of  thin, 
double-stained  sections  of  human  liver  (No. 
1 23)  for  from  two  to  three  minutes  in  a  test- 
tube  half  filled  with  distilled  water.  The 
liver  cells  in  part  fall  out ;  examine  the 
edges  of  the  preparation  in  a  drop  of  water 
(Fig.  233).  This  preparation  can  be  mounted  in  xylol-balsam,  but  the 
more  delicate  connective-tissue  fibers  disappear  therein. 


Fig.  233. — From  a  Shaken  Section  of 
A  Human  Liver.  X  240.  c.  Blood 
capillaries,  at  x  still  containing  blood 
corpuscles.  6,  Interlobular  connec- 
tive tissue.  On  the  right  side  are  five 
hepatic  cells;  the  others  have  fallen 
out  of  the  meshes  of  the  capillary  net- 
work. 


*  For  the  study  of  the  structure  of  the  gall-bladder,  as  well  as  of  the  larger  bile-ducts, 
only  absolutely  fresh  tissue  can  be  used,  since  the  alkaline  bile  soon  after  death  saturates  the 
wall  of  the  gall-bladder,  stains  it  yellow,  and  makes  it  unfit  for  microscopic  investigation. 


THE    DIGESTIVE    ORGANS.  3O7 

No.  125. — Blood-vessels  of  the  liver. 

{(X)  Chloroform  a  rabbit  and  quickly  place  a  2  cm.  cube  of  liver 
(without  allowing  much  blood  to  flow  from  it)  in  50  c.c.  of  absolute  alco- 
hol. In  two  days  the  natural  injection  can  be  seen  on  the  surface  ;  it  is 
indicated  by  brown  spots  at  the  center  of  the  lobules.  Cut  thick  sec- 
tions parallel  to  the  surface  and  mount  them  unstained  in  xylol-balsam. 
Examine  with  a  low  power.  Very  frequently  only  the  superficial  strata 
of  the  liver  contain  filled  blood-vessels. 

{U)  Of  all  injections  that  of  the  liver  is  most  easily  accomplished. 
Inject  Berlin  blue  (p.  48),  either  through  the  portal  vein  or  the  inferior 
vena  cava  ;  in  the  latter  case  it  is  advisable  to  make  an  incision  above 
the  diaphragm  ;  allow  the  heart  to  rest  upon  the  latter  and  insert  the 
canula  through  the  right  auricle  into  the  inferior  cava.  The  injected 
liver  is  to  be  placed  in  toto  in  about  500  c.c.  of  Miiller's  fluid  ;  after  six 
days  pieces  about  2  cm.  square  of  the  portions  best  injected  are  to  be  cut 
out,  again  placed  for  two  or  three  weeks  in  about  150  c.c.  of  Miiller's 
fluid,  and  finally  hardened  in  100  c.c.  of  gradually  strengthened  alcohols. 
Cut  thick  sections  and  mount  them  unstained  in  xylol-balsam  (Figs.  223, 
224,  226). 

No.  1 26. — Exhibition  of  gland  hiniina  by  Golgi's  "  black  reaction^ — 
Place  small  pieces  of  the  root  of  the  tongue,  of  the  stomach,  of  the  salivary 
glands,  and  of  the  liver  for  three  days  in  the  potassium-bichromate- 
formol  mixture  and  then  in  the  silver  solution.  For  further  treatment  see 
page  45.  Very  often  the  staining  does  not  succeed  until  after  the  procedure 
has  been  repeated  once  or  twice.  After-staining  (p.  47)  is  strongly  advised. 
In  the  liver  the  "  lattice-fibers  "  occasionally  stain. 

No.  127. — EpitJieliiini  of  the  peritoneum. — Proceed  as  in  No.  40,  p. 
153,  but  instead  of  taking  the  mesentery,  which  also  yields  instructive 
pictures,  use  the  greater  omentum.  The  pieces  may  be  stained  in  Han- 
sen's hematoxylin  (p.  38)  and  mounted  in  xylol-balsam  (Fig.  228). 


308  HISTOLOGY. 

VI.     THE    RESPIRATORY   ORGANS. 

The    Larynx. 

The  imicons  membrane  of  the  larynx  is  a  continuation  of  the  pharyn- 
geal mucous  membrane  and  like  this  is  composed  of  an  epithelium,  a 
tunica  propria,  and  a  submucosa,  which  latter  connects  the  mucous 
membrane  with  the  underlying  parts.  The  epithelium  over  nearly  the 
whole  of  the  organ  is  a  many-row  (p.  jy^  ciliated  epithelium  ;  the  ciliary 
wave  is  directed  toward  the  cavity  of  the  pharynx.  On  the  true  vocal 
cords,  on  the  anterior  surface  of  the  arytenoid  cartilages,  and  on  the  laryn- 
geal surface  of  the  epiglottis  the  epithelium  is  of  the  stratified  squamous 
variety.  The  tunica  propria  consists  of  numerous  elastic  fibers  and  ot 
fibrillar  connective  tissue,  which  in  the  lower  animals  is  condensed  to  a 
membrana  propria  immediately  beneath  the  epithelium.  The  tunica 
propria  is  the  site  of  a  varying  number  of  leucocytes  ;  even  solitary 
nodules  (p.  146)  are  found  in  the  mucous  membrane  of  the  ventricle  of 
the  larynx  (Morgagni).  Papillae  mainly  occur  in  the  mucous  membrane 
clothed  with  stratified  squamous  epithelium  ;  on  the  free  border  and  on 
the  lower  surface  of  the  vocal  cords  the  papillae  are  merged  in  longitu- 
dinal ridges.  On  the  laryngeal  surface  of  the  epiglottis  only  isolated 
papillae  are  present,  on  which  are  short  taste-buds.  The  submucosa  con- 
tains branched  alveolo-tubular  glands,  from  0.2  to  i  mm.  in  size  ;  the 
middle  of  the  vocal  cords  for  a  certain  distance  from  the  free  edge  is 
without  glands. 

The  cartilages  of  the  larynx  principally  consist  of  the  hyaline  variety, 
which  in  a  measure  exhibits  the  peculiarities  of  the  costal  cartilages  (p. 
97).  The  hyaline  cartilages  are  the  thyroid,  the  cricoid,  the  greater 
portion  of  the  arytenoids,  and  often  the  triticeous  cartilages.  The  epi- 
glottis, the  cuneiform  cartilages  (Wrisbergi),  the  cornicular  cartilages 
(Santorini),  the  median  portion  of  the  thyroid,  and  the  apex  and  vocal 
process  of  the  arytenoid  cartilages  are  of  the  elastic  (fiber-net)  variety. 
Occasionally  the  triticeous  cartilages  are  composed  of  fibro-cartilage. 
Between  the  twentieth  and  thirtieth  years  of  life  ossification  (chiefly  endo- 
chondral) begins  in  the  thyroid  and  cricoid  cartilages. 

The  larynx  is  richly  supplied  with  blood-vessels  and  nerves.  The 
blood-vessels  form  two  or  three  networks  extending  in  planes  parallel  to 
the  surface  and  a  close  subepithelial  capillary  plexus. 

The  lymph-vessels  form  two  anastomosing  networks  also  extending 
in  horizontal  planes,  of  which  the  superficial  consists  of  narrower  vessels 
and  lies  beneath  the  blood  capillary  network. 


THE    RESPIRATORY    ORGANS.  309 

The  nerves  include  microscopic  ganglia  in  their  course  and  form  a 
deep  and  a  superficial  plexus.  The  nonmedullated  nerves  end  partly  as 
little  subepithelial  terminal  trees,  the  twigs  of  which  are  provided  with 
enlargements,  or  in  end-bulbs,  and  partly  intraepithelial  in  free  branches 
and  in  tastebuds  (see  the  Gustatory  Organ).  Below  the  vocal  cords  sub- 
epithelial nerve -endings  and  buds  are  wanting  ;  but  many  intraepithelial 
nerve-fibers  are  present,  that  spin  networks  about  the  individual  gus- 
tatory cells. 

The  Trachea. 

The  ciliated  mucous  membrane*  of  the  trachea  possesses  a  structure 
like  that  of  the  larynx,  excepting  only  that  the  elastic  fibers  form  a  close 
network  in  which  the  fibers  pursuing  a  longitudinal  direction  predomi- 
nate. This  network  lies  immediately  beneath  the  epithelium  and  above 
the  mixed  glands.  The  cartilages  are  of  the  hyaline  variety.  The  pos- 
terior wall  of  the  trachea  is  composed  of  a  layer  of  transversely  arranged 
smooth  muscle-fibers,  that  usually  is  covered  by  a  stratum  of  muscle-fibers 
extending  longitudinally. f  The  glands  of  the  posterior  wall  are  distin- 
guished by  their  size  (2  mm.)  ;  they  not  infrequently  penetrate  the  mus- 
cular layer,  so  that  they  lie  in  part  in  the  fibrous  tissue  behind  it. 

The  behavior  of  the  blood-vessels,  lymph-vessels,  and  nerves  is  the 
same  as  in  the  larynx  ;  the  nerve-fibers  ending  on  the  smooth  muscle- 
fibers  of  the  trachea  are  nonmedullated  and  come  from  the  nerve-cells  ot 
the  small  (sympathetic)  ganglia  ;  the  sensory  nerve-fibers  are  medullated 
and  of  cerebrospinal  origin  (?  </.  remark  f,  p.  219). 

The  Bronchi  and  the  Lungs. 
The  lungs  may  be  regarded  as  compound  alveolo-tubular  glands,  in 
which,  as  in  all  glands,  excretory  and  secretory  (in  this  case  respiratory) 
divisions  are  distinguished.  The  excretory  division  comprises  the  larynx 
and  the  trachea  with  its  branches,  the  bronchi.  Each  bronchus  on  en- 
tering the  lung  divides  repeatedly  and  within  the  same  undergoes  con- 
tinual subdivision,  by  the  direct  giving  off  of  small  lateral  twigs  and  by 
the  branching  at  acute  angles  with  gradual  decrease  in  the  caliber  of  the 
large  branches  ;  in  this  way  each  bronchus  breaks  up  into  minutest  twigs, 
that  nowhere  anastomose  with  one  another  and  that  retain  the  character 
of  the  excretory  duct  to  a  diameter  of  0.5  mm. 

*  The  mucous  membrane  which  covers  the  posterior  wall  of  the  trachea  appears  to  vary  ; 
at  least  I  have  found  there,  in  the  mucous  membrane  of  a  healthy  man,  stratified  squamous 
epithelium  and  a  tunica  propria  with  papilla;. 

f  The  smooth  musculature  of  the  trachea  and  its  branches  is  as  richly  provided  with  elas- 
tic fibers  as  that  of  the  intestine  (p.  275). 


3IO 


HISTOLOGY. 


At  this  point  the  respiratory  division  begins.  Isolated  hemispher- 
ical evaginations,  tlie  alveoli,  appear  at  irregular  intervals  on  the  walls  of 
the  minute  bronchial  branches.  Such  bronchial  branches  are  called 
respiratory  bronchioles.  These  divide  and  lead  into  the  alveolar  ducts, 
which  differ  from  the  bronchioles  only  in  being  completely  encircled  by 
alveoli.  The  alveolar  ducts  divide  at  right  or  acute  angles  and  pass 
without  sharp  demarcation  into  the  slightly  expanded,  blind  alveolar 
sacks  or  terminal  vesicles  (less  correctly,  infundibula),  the  walls  of  which 


Bronchial  artery.— 


Pulmonary  vein 


—  -»  Pulmonary  artery 


■  Respiratory  bronchiole. 


-'Alveolar  duct. 


Pleurarcapillaries 


-'\\ : Alveolar  sack . 

) 

^^U*  P  CHE  N 


(Lobule.) 


Fig.  234. — Scheme  of  the  Terminal  Ramifications  of  the  Human  Bronchial  Tree  and  its  Blood- 
vessels. 

are  thickly  beset  with  alveoli.*  Each  alveolus  is  open,  not  only  toward 
the  alveolar  sack, — this  broad  opening  is  termed  base — but  also  is  in 
direct  communication  with  neighboring  alveoli  by  means  of  a  widely 
varying  number  of  minute  canals,  the  so-called /(^r^-jr  (Fig.  237  B). 

The  entire   respiratory   division    is  separated    by  connective  tissue 
into  lobides  from  0.3  to  3  sq.  cm.  in  size.      All  the  branches  of  the  ex- 


*To  describe  as  atrium  a  special  division  between  the  alveolar  duct  and  the  alveolar  sack 
appears  to  me  superfluous ;  it  cannot  be  distinguished  in  good  molds  of  the  human  lung. 


THE    RESPIRATORY    ORGANS. 


311 


cretory  division  down  to  a  diameter  of  from  1.5  to  i  mm.  lie  bcttveeii  the 
lobules,  are  interlobular. 

The  minute  structure  of  the  bronchi  diwd  their  largest  branches  does 
not  differ  from  that  of  the  trachea.  Gradually  modifications  appear,  which 
first  involve  the  cartilages  and  the  musculature.  The  C-shaped  ring  car- 
tilages are  replaced  by  irregular  plates,  lying  on  all  sides  of  the  bronchial 
wall.     They  diminish  in  size  and  thickness  with  the  decrease  in  the  diam- 


Tunic.a 
Epithelium.  propria 


Nerve. 


Blood- 


vessel 
Fat-cells 


Cartilage. 


-Alveoli. 


Fibrous  membrane 


Gland 


Excretory  duct  of 
gland. 


Fig.  235.— Cross-section  of  a  Bronchial  Branch,  Two  Millimeters  Thick,  of  a  Child.     X  30.    Technic 

No.  128  a. 


eter  of  the  bronchial  branches  and  disappear  in   the  branches  i  mm.  in 
diameter. 

The  smooth  muscle-fibers  are  circularly  disposed  in  a  continuous  layer 
lying  within  the  cartilages  and  embracing  the  entire  circumference  of  the 
tube.  The  thickness  of  the  muscular  layer  decreases  with  the  diameter 
of  the  bronchial  branches  ;  but  muscle-fibers  are  still  present  in  the  alve- 
olar ducts.      They  are  wanting  in  the  alveolar  sacks. 


312 


HISTOLOGY. 


The  mucous  membrane  is  thrown  into  longitudinal  folds  and  con- 
sists of  a  many-rowed  ciliated  epithelium  containing  goblet-cells,  that  in 
the  minute  bronchial  branches  becomes  gradually  reduced  to  a  single- 
row  epithelium,  and  of  a  connective-tissue  tunica  propria.  The  latter 
contains  a  network  of  numerous  longitudinally  disposed  elastic  fibers  and 
leucocytes  in  greatly  varying  number.  Occasionally  the  latter  form  soli- 
tary nodules,  from  the  crest  of  which  leucocytes  wander  through  the 
epithelium  into  the  bronchial  tube. 

Branched  alveolo-tubular  mixed  glands  occur  as  far  as  the  cartilages 
extend  ;  they  are  situated  outside  of  the  muscular  layer  (Fig.  235).  They 
are  numerous  and  do  not  disappear  until  at  the  beginning  of  the  respi- 
ratory bronchioles. 

Terminal  bronchiole 


Alveoli 


Alveolar  duct 


Fig.  236. — From  a  Section  of  the  Lung  of  Adult  Man.  X  so.  The  terminal  bronchiole  divides  into  two 
branches  (on  the  right).  A  portion  of  the  wall  of  the  bronchiole  fell  within  the  plane  of  the  section  ;  here 
the  entrance  to  the  alveoH  is  seen  from  above  ;  in  the  lower  branch  the  alveoli  are  viewed  from  the  side. 
The  epithehum  of  the  bronchiole  is  mixed.  The  epithehal  outfit  of  the  alveoli  is  only  partially  visible  with 
this  magnification.     Technic  No.  129. 


External  to  the  cartilages  is  z.  fibrous  membrane  consisting  of  fibrous 
connective  tissue  and  elastic  fibers,  which  envelops  the  entire  bronchus, 
including  the  accompanying  vessels  and  nerves. 

The  minute  structure  of  the  respiratory  division,  after  the  gradual  dis- 
appearance of  cartilages  and  glands,  is  distinguished  in  particular  by  the 
nature  of  the  epithelium. 

The  respiratory  bronchioles,  succeeding  the  smallest  bronchial 
branches,  at  their  beginning  still  contain  a  layer  of  single-row  ciliated  epi- 
thelium ;  in  their  further  course  the  cilia  are  lost,  the  cells  become  cubical, 
and  between  these  another  kind  of  epithelial  cell  appears,  in  the  form  of 
thin  nonnucleated  plates  of  different  sizes.  These  plates  and  isolated  or 
small  groups  of  cubical  cells  form  an  epithelium  called  respiratory  epithe- 
lium. The  transition  of  the  cubical  epithelium  into  the  respiratory  epithe- 
lium is  not  abrupt,  but  occurs  in  such  wise  that  on  the  one  side  of  the 


THE    RESPIRATORY    ORGANS. 


313 


bronchiole  cubical,  on  the  other  side  respiratory  epithelium  is  found,  or 
that  groups  of  cubical  cells  are  surrounded  by  respiratory  epithelium  and 
the  reverse.  Hence  the  respiratory  bronchioles  contain  a  mixed  epithe- 
lium (Fig.  236  and  Fig.  237  A).  Since  the  respiratory  epithelium  steadily 
gains  in  extent  and  the  groups  of  cubical  cells  become  steadily  less  fre- 
quent, the  epithelium  of  the  bronchioles  changes  into  that  of  the  alveolar 
ducts. 

The  epithelium  of  the  alveolar  ducts  and  of  the  alveoli  is  the  same 
as  the  respiratory  epithelium  of  the  bronchioles.  The  developmental 
history  teaches  that  the  smaller  nonnucleated  plates  originate  from 
cubical  epithelial  cells,  that  become  flattened  by  inspiration,  that  is,  by  the 
complete  stretching  of  the  alveolar 

wall.   The  larger  plates  are  formed  p°"^-   CuWcai  epithelial  ceiis 

by  the  subsequent  blending  of  sev-  -  ^\"**v^'^  *l*'^ 


'\).%T 


/  \ 


o-.,^ 

V\/'>    I- 

■  <■ 

^Vsi  t 

\/-v--    J 

Q 

//>"'•'    ,1 

^\'  ■   \ 

r^' 


/ 


'  Border  of  an  alveolus.        B        Fundus  of  an  alveolus. 

Fig.  237. — From  Sections  of  a  Human  Lung.  X  240.  A.  Mixed  epithelium  of  a  respiratory  bronchiole.  B. 
An  alveolus  sketched  with  change  of  focus.  The  border  of  the  alveolus  is  shaded;  it  is  covered  by  the  same 
epithelium  as  that  of  the  (clear)  fundus  of  the  alveolus',;  the  nuclei  of  the  cells  are  invisible.     Technic  No.  129. 

eral  smaller  ones.  The  alveoli  of  old  embryos  and  of  stillborn  children 
contain  only  cubical  cells.  The  walls  of  the  alveolar  ducts  and  of  the 
alveoli,  in  addition  to  the  previously  mentioned  muscle-fibers  in  the  for- 
mer, are  composed  of  a  delicately  striated  ground  layer  and  many  elastic 
fibers.  The  latter  are  circularly  arranged  in  the  alveolar  ducts  ;  at  the 
entrance  ("base")  to  the  alveolus  the  elastic  fibers  form  a  thick  ring, 
while  delicate,  convoluted  little  fibers  occur  in  the  entire  wall  of  the  alve- 
olus (Fig.  238).  The  elastic  rings  of  neighboring  alveoli  grow  together 
at  the  points  of  contact  and  form  the  alveolar  septa. '^ 


*This  wealth  of  elastic  fibers  enables  the  alveolus  to  expand  during  inspiration  to  three 
times  its  usual  diameter  and  during  expiration  to  return  again  to  its  original  diameter  of  from 
o.  I  to  0.3  mm. 


314 


HISTOLOGY. 


The  intej'lobular  connective  tissue  occurring  between  the  lobules  of 
the  lungs  supports  the  larger  blood-  and  lymph-vessels  and,  besides  fine 
elastic  fibers  and  a  few  connective-tissue  cells,  in  the  adult  contains  black 
pigment  granules  and  minutest  particles  of  carbon,  that  have  come  there 
by  inhalation.  In  children  the  interlobular  connective  tissue  is  more 
richly  developed  and  therefore  the  demarcation  of  the  lobules  is  more 
distinct. 

The  surface  of  the  lung  is  covered  by  the  visceral  pleura ;  this  is 
composed   of  connective-tissue,  numerous    fine  elastic   fibers,  and  on  its 


Elastic  rings 


Alveolar  duct.  Alveoli.  Alveolar  septa. 

Fig.  238. — Section  of  the  Lung  of  a  Rabbit.     X  220.    Stained  elastic  fibers.    Technic  No.  130  h. 

free  surface  is  clothed  with  a  simple  stratum  of  flat,  polygonal  epithelial 
cells.*  The  parietal  pleura  has  the  same  structure,  but  contains  fewer 
elastic  fibers. 

The  lungs  have  two  systems  of  blood-vessels :  i,  the  system  of  pul- 
monary arteries  and  veins,  serving  the  purposes  of  respiration  ;  2,  the 
system  of  bronchial  arteries  and  veins.  The  branches  of  \he  piihnonary 
artery  penetrate  at  the  hilus  of  the  lung  and  run  beside  the  bronchial 
branches  in  the  lobules  to  the  bronchioles,  alveolar  ducts,  and  alveolar 


*  In  the  dog  and  the  rabbit  they  are  provided  with  a  delicate  hair  border. 


THE    RESPIRATORY    ORGANS.  315 

sacks  ;  where  they  break  into  a  very  narrow-meshed  capillary  plexus, 
lying  immediately  beneath  the  respiratory  epithelium  of  the  alveoli,  alve- 
olar ducts,  and  respiratory  bronchioles  and  communicate  with  a  wide- 
meshed  capillary  net  lying  under  the  pulmonary  pleura.  T\\q  pulmonary 
veins  arise,  one  each  at  the  base  of  an  alveolus  (Fig.  239),  take  up  on 
the    surface    of   the   lung  veins 

from  the  capillaries  of  the  pleura,  ^      ^      ^^^k^^:^ ^''^''i- 

and  collect  in  small  trunks  that 
run  at  the  periphery  of  the  lob- 
ules and  only  later  approach  the 
larger  bronchial  branches.  The 
brojichial  arteries  provide  for  the 

1  I.  •    1  •  c      ^-  i      iU  Fig.  2^0. — From  a  Section  of  the  Lung  of  a  Child, 

bronchial  ramifications  up  to  the        "-  i/j^cted  through  the  PuLiioxARY  artery,    x  80. 

,  1   ■     1  1  Of  the    five  alveoli  drawn  the    three  upper    ones  are 

respiratory  bronchioles  and  sup-  fully  injected.   Technic  Xo.  131. 

ply  a  deep  capillary  plexus  for 

the  glands  and  muscles  and  a  superficial  plexus  for  the  tunica  propria  ; 
also  the  walls  of  the  pulmonary  arteries  and  veins,  the  bronchial  lymph- 
glands,  and  the  pulmonary  pleura  receive  branches  from  the  bronchial 
arteries.  The  bronchial  veins  empty  their  blood  partly  into  the  pulmon- 
ary veins  (Fig.  234  x),  partly  in  the  territory  of  the  azygos  vein.  Large 
and  small  anastomoses  exist  between  the  pulmonary  and  bronchial  arteries. 

The  lymph-vessels  form  a  superficial  and  a  deep  plexus  ;  the  well- 
developed  S7iperfieial  plexus,  lying  beneath  the  pleura,  is  connected  with 
pea-sized  lymph-nodes  irregularly  distributed  under  the  pulmonary 
pleura,  and  opens  by  several  small,  valved  trunks  into  the  bronchial 
lymph-glands.  The  wide-meshed  deep  plexus,  situated  in  the  interlob- 
ular connective  tissue,  collects  the  lymph-vessels  of  the  bronchial 
mucous  membrane*  and  of  the  walls  of  the  blood-vessels  ;  from  this 
small,  valved  trunks  proceed  which,  running  with  the  bronchial  ramifi- 
cations, pass  out  at  the  hilus  and  there  open  in  the  bronchial  lymph- 
glands  {cf.  p.  141). 

The  numerous  nerves  of  the  lungs,  originating  from  the  sympa- 
thetic and  the  vagus,  contain  medullated  and  nonmedullated  nerve-fibers 
and  small  groups  of  ganglion  cells.  The  nerve  endings  stand  chiefly  in 
relation  to  the  blood-vessel  walls. 

The  Thyroid    Gland. 

The  thyroid  gland  arises  essentially  from  a  median  proliferation  of 
the  ventral  wall  of  the  esophagus  and  at  first  has  the  appearance  of  a 


*  Lymph-vessels  are  not  present  in  the  alveolar  ducts  and  alveolar  sacks  (of  the  dog). 


3i6 


HISTOLOGY. 


tubular,  compound,  retiform  gland  ;  its  excretory  duct,  the  tliyro-glossal 
duct,  opening  at  the  foramen  caecum  of  the  tongue,  becomes  obliterated 
in  an  early  embryonal  period  and,  excepting  a  few  fragments,  atrophies 
and  disappears  ;  the  network  of  gland  tubules,  that  at  first  are  not 
hollow,  becomes  constricted  into  short  pieces,  "follicles,"  which  are 
bound  together  in  lobules  by  loose  connective  tissue  interlaced  with 
elastic  fibers.  In  adult  man  the  follicles  are  oval  sacks  blind  at  both  ends, 
differing  greatly  in  diameter  (from  40  to  120  //),  and  clothed  with  a 
simple  layer  of  sometimes  cubical,  sometimes  cylindric  epithelial  cells, 
that  in  man  contain  granules  of  a  partially  fatty  nature.     The  lumen  of 


Colloid  substance 


Epithelium 


Fig.  240. — A  Lobule  from  a  Thin  Section  of  the  Thyroid  Gland  of  Adult  Man. 
ference  in  the  diameter  of  the  tubules.     Technic  No.  132. 


Tangential  section  of 
a  tubule  ;  the  epi- 
thelium \dewed 
from  the  surface. 


Tubule  in  transverse 
section. 


Connective  tissue. 
X  220.    Note  the  dif- 


the  sack  is  filled  with  a  homogeneous,  viscid  mass,  the  colloid  stibstance,  a 
product  of  the  epithelial  cells.*  The  very  numerous  blood-vessels  form  a 
capillary  plexus  enveloping  the  follicles  and  lying  close  beneath  the  epi- 
thelium. The  equally  numerous  lymph-vessels  form  a  network  lying  be- 
tween the  follicles.     The  nerves  run  with  the  ramifications  of  the  blood- 


*  Formerly  the  colloid  substance  was  credited  as  a  characteristic  of  the  thyroid  gland; 
but  since  masses  resembling  the  colloid  have  been  found  in  the  hypophysis  (p.  208),  and 
since  in  the  blood-  and  lymph-vessels  of  the  throat  the  coagulated  blood  may  very  closely  re- 
semble the  colloid,  this  sign  loses  its  diagnostic  value.  The  manner  in  which  the  secretion  pro- 
duced by  the  thyroid  gland  is  discharged  is  not  yet  clear.  It  has  been  observed  that  at  all  the 
nodal  points  of  the  net  of  terminal  bars  the  cement  substance  is  wanting  ;  perhaps  this  is  an 
instance  of  the  sundering  of  the  epithelial  cells  to  permit  the  passage  of  the  secretion  to  the 
lymph  channels.  Possibly  the  secretion  is  taken  up  by  the  blood-vessels.  That  the  secretion 
plays  an  important  part  in  the  economy  of  the  body,  by  rendering  poisonous  products  of  metab- 
olism innocuous,  has  been  established  by  experiment. 


THE    RESPIRATORY    ORGANS.  317 

vessels  and  form  an  enveloping  plexus,  chiefly  for  the  vessels,  partly  also 
for  the  gland  sacks.  The  penetration  of  terminal  twigs  into  the  epithe- 
lium has  not  been  observed. 

On  the  posterior  surface  of  each  lateral  lobe  of  the  thyroid  gland  are 
found  from  one  to  four  "  epithelial  corpuscles,"  two  millimeters  in  size;  they 
consist  of  cords  or  nests  of  epithelial  cells,  that  surrounded  by  blood  capil- 
laries and  connective  tissue  have  arisen  from  the  visceral  clefts.  In  different 
mammalian  animals,  embryos  and  adults,  there  has  been  found  in  each  lateral 
lobe  of  the  thyroid  gland  a  duct  lined  with  squamous  to  cylinder  ciliated  epi- 
thelium, the  central  canal' of  the  thyroid  ghind,  that  is  connected  with  the  sur- 
rounding gland  lobules  and  the  epithelial  corpuscles. 

The  Thymus. 
The  thymus  arises  paired  out  of  the  epithelium  of  the  third  visceral 
cleft ;    the    originally    hollow   evagination    sends    out    solid    branching 


Cortex. 


Medulla. 


/         7^         ^  ^    '    J' 

Connective  tisstie.  /  ""iS-  ''^ 

Blood-vessels. 

Fig.  241. — Section  of  several  Secotoary  Lobules  of  the  Thymus  of  a  Seven-Day-Old  Rabbit.     X  50. 
The  lower  lobules  are  sectioned  tangentially,  so  that  chiefly  cortex  is  \-isible.     Technic  Xo.  133. 

sprouts,  in  the  vicinity  of  which  conspicuous  masses  of  adenoid  tissue 
develop  ;  numerous  leucocytes  wander  from  here  into  the  epithelium 
and  make  rents  through  which  also  the  blood-vessels  and  connective 
tissue  penetrate.  During  childhood  the  thymus  consists  of  lobes  from  4 
to  1 1  mm.  in  size;  fibrous  connective  tissue  intermixed  with  delicate 
elastic  fibers  sends  septa  in  each  individual  lobe,  whereby  a  subdivision 
in  smaller,  one  millimeter  square  ("  secondary  ")  lobules  is  effected.  The 
lobules  are  connected  by  means  of  a  "  medullary  cord,"  from  i  to  3  mm. 
in  thickness.  The  appearance  of  these  lobules  varies  greatly  ;  occasion- 
ally each  lobule  consists  wholly  of  adenoid  tissue,  which  is  more  densely 
developed  at  the  periphery  than  in  the  center,  so  that  a  darker  cortical 


3i8 


HISTOLOGY. 


portion  can  be  distinguished  from  a  lighter  medullary  substance  (Fig. 
241).  In  these  cases,  owing  to  the  extensive  wandering  in  of  the  leuco- 
cytes, the  epithelium  has  almost  entirely  disappeared.  In  other  cases, 
particularly  in  man,  the  medullary  substance  contains  larger  or  smaller 


Cortical  substance 


Medullary  sub 
stance. 


Connective  tissue 


,'■'  Transverse  section 
— "■      of  blood-vessel. 


_j  Medullary  cord. 


Fig.  242. — Transverse  Section  or  a  Portion  of  the  Thymus  of  a  Child  One  and  Three-quarter  Years 

Old.     X  21.    Techniclvro.  133. 

groups  of  epithelial  cells,  that  not  infrequently  are  penetrated  by  wander- 
ing leucocytes,  and  also  the  branches  of  the  medullary  cord  often  con- 
sist of  distinct  epithelial  cells  (Fig.  242). 

The  medullary  substance  and  medullary  cord  are  the  site  of  con- 
centrically striated  corpuscles,  of  from  15  to  180//  in  diameter,  which 
are  altered  balls  of  epithelial  cells.*     These   "corpuscles   of   Hassal" 

(Fig.  243)  increase  in  size  and 
number  after  birth  and  can  still 
be  found  in  the  remains  of  the 
thymus  in  adults. 

The  arteries  run  between  the 
cortex  and  the  medulla  and  feed 
capillaries  which   chiefly   develop 
in  the  former,  in  the  latter  only 
where  it  is  not  composed  of  epithe- 
lium.      The  veins  collecting  from 
the  latter  partly  run  in  the  medulla, 
partly  they  empty  in  large  venous  stems  lying  between  the  lobules.      The 
numerous  lymph-vessels  arise  from  wide  lymph  spaces  lying  immediately 
on  the  surface  of  the    lobules  and  form  large  stems  lying  in  the  inter- 


Nuclei  of  the  epithelial  cells. 


©©*30 


Leucocytes.  <S 


Corpuscle  of  Hassal. 


Fig.  243. — Corpuscle  of  Hassal  from  a  Section 
OF  the  Thymus  of  a  Young  Dog.  X  560. 
Technic   Ko.  133. 


*  Also  structures  resembling  the   epithelial  corpuscles  of  the  thyroid  gland  are  said  to 


THE    RESPIRATORY    ORGANS.  3I9 

lobular  connective  tissue,  that  subsequently  proceed  as  valved  vessels 
alongside  the  larger  blood-vessels.  The  nerves  end  chiefl}-  on  the 
blood-vessels,  only  an  extremely  few  small  fibers  penetrate  the  medulla, 
where  they  terminate  in  free  ends. 

The  atrophy  of  the  thymus,  of  which  the  period  of  onset  is  ex- 
tremely variable,  takes  place  in  such  wise  that  the  larger  portion  of  the 
adenoid  tissue  vanishes  and  fat  appears  in  its  place.  Not  only  leucocytes, 
but  also  colored  blood-cells  arise  in  the  adenoid  tissue.  Hematoblasts 
(p.  140)  also  have  been  found  in  it. 

TECHMC. 

No.  128. — The  larvxx,  the  bronehi,  a/id  the  thxroiel  s;-land. — Of 
animals  the  adult  cat  is  particularly  recommended.  Expose  the  trachea 
above  the  manubrium  ;  cut  it  and  the  esophagus  through  transversely  and 
dissect  both  loose  upwards  (see  No.  103,  p.  298).  The  tongue  ma\-  be  re- 
moved with  these  parts.  The  thyroid  gland  should  be  allowed  to  remain 
attached  to  the  larynx.  The  whole  is  placed  for  from  two  to  six  weeks 
in  200  or  400  c.c.  of  Miiller's  fluid,  then  washed  for  one  hour  in  running 
water  and  hardened  in  200  c.c.  of  gradually  strengthened  alcohols 
(P-  35)-  -f^  about  eight  daj  s  cut  sections,  transverse  and  longitudinal, 
through  the  vocal  cords  and  through  pieces  of  the  trachea;  stain  them 
for  five  minutes  in  Hansen's  hematoxylin  (p.  38)  and  mount  in  xylol- 
balsam.  Particularly  instructixe  are  sections  taken  transversely  through 
the  vocal  cords,  in  which  the  mucous  membrane,  glands,  muscles,  blood- 
vessels, nerves,  and  cartilage  aftbrd  the  most  varied  stud\'.  \'ery  beau- 
tiful pictures  are  obtained  by  staining  the  sections  with  borax-carmine 
(p.  40)  and  with  resorcin-fuchsin  (No.  13,  p.  43). 

No.  12S  a. —  The  bronchi. — From  an  animal  just  killed  (rabbit)* 
remove  the  lungs,  fix  them  in  Miiller's  fluid  and  harden  them  in  gradu- 
ally strengthened  alcohols,  like  No.  128.  In  eight  days  cut  out  of  the 
lung  I  cm.  cubes  that  contain  a  portion  of  a  longitudinally  disposed 
bronchus.  With  the  scissors  remove  the  greater  part  of  the  attached 
lung  tissue;  embed  the  bronchus  in  liver  and  make  thin  transverse 
sections,  which  may  be  stained  in  Hansen's  hematoxylin  (p.  38)  or  after 
No.  13,  p.  43,  and  mounted  in  x\-lol-balsam  (Fig.  235).  This  method 
is  also  applicable  for  the  exhibition  of  the  alveoli  and  the  alveolar  pas- 
sages. 

No.  129. — The  respiratory  epitheliittn. — For  the  demonstration  of 
this  tissue  only  animals  just  killed  can  be  used.  Young  kittens  {not 
newborn)  are  suitable;  they  should  be  killed  by  decapitation.  The 
trachea  and  lungs  should  be  carefully  taken  out  and  filled  by  means  ot  a 
glass  pipet  with  a  pre\iously  prepared  solution  of  silver  nitrate  (50  c.c. 

*  The  lungs  of  cats  are  less  suitable,  because  of  the  conspicuous  masses  of  fat  that  often 
accompany  the  bronchial  branches. 


320  HISTOLOGY. 

of  a  I  per  cent,  solution  to  200  c.c.  of  distilled  water).  The  trachea 
should  then  be  tied  fast  and  the  whole  placed  for  from  one  to  twelve 
hours  in  the  remainder  of  the  silver  solution  and  stood  in  the  dark.  On 
removing  them  from  the  silver  solution  the  lungs  should  be  quickly 
washed  with  distilled  water  and  transferred  to  150  c.c.  of  gradually- 
strengthened  alcohols,  in  which  they  may  remain  (in  the  dark)  indefinitely. 
The  reduction  can  be  undertaken  in  an  hour  after  the  silver  injection  or 
later.  For  this  purpose  the  lungs  in  the  alcohol  should  be  exposed  to 
sunlight,  in  which  in  a  few  minutes  they  become  a  deep  brown.  Then 
with  a  veiy  sharp  razor  cut  sections,  taking  care  not  to  compress  the 
tissue.  Despite  the  hardening  in  alcohol  the  lung  tissue  is  still  soft  and 
allows  only  thick  sections  to  be  cut.  Sections  are  most  easily  cut  in  a 
direction  parallel  to  the  surface.  Place  the  sections  for  from  ten  to  sixty 
minutes  in  5  or  10  c.c.  of  distilled  water  to  which  a  crystal  of  common 
salt  about  the  size  of  a  lentil  has  been  added,  and  mount  them  unstained 
in  xylol-balsam.  (It  is  not  advisable  to  employ  nuclear  staining,  since 
not  only  the  nuclei  of  the  epithelial  cells,  but  also  those  of  the  capillaries 
and  other  tissues  are  colored,  and  consequently  the  picture  becomes  very 
complicated.)  Orientation  in  such  sections  is  not  altogether  easy.  The 
investigation  should  be  begun  with  the  low  power.  The  small  alveoli 
are  easily  recognized  ;  the  somewhat  larger  spaces  correspond  to  alveolar 
ducts.  The  outlining  of  the  epithelium  is  on  the  whole  finer  with  medium 
magnification  (80  diameters),  and  by  no  means  equally  good  in  all  places. 
The  cubical  epithelial  cells  are  usually  colored  a  somewhat  deeper  brown. 
Find  a  good  place,  study  it  with  the  high  power  (240  diameters),  and  by 
changing  the  focus  (elevating  and  depressing  the  tube)  practice  orienta- 
tion in  the  relief  of  the  preparation;  with  high  magnification,  either  only 
the  interior  or  the  margin  of  an  alveolus  can  be  distinctly  seen.  Fig. 
237  i?  was  drawn  with  change  of  focus.  The  pores  of  the  alveoli  can 
not  be  demonstrated  on  each  alveolus. 

No.  130. — Elastic  fibers  of  the  lungs,  («)  fresh. — With  the  scissors 
placed  on  a  freshly  cut  surface  of  the  lung  (the  lung  need  not  be  fresh), 
cut  a  flat  piece  about  i  cm.  square,  spread  it  out  with  needles  on  a  dry 
slide,  apply  a  cover-glass  and  treat  it  with  two  drops  of  potash  lye  (p.  23) 
diluted  one-half  with  water;  the  diluted  lye  destroys  all  parts  excepting 
only  the  elastic  fibers,  the  thickness  and  arrangement  of  which  can  be 
easily  investigated  with  the  high  power  (240  diameters). 

{b)  For  permanent  preparation. — Fix  i  or  2  cm.  cubes  of  lung  in 
absolute  alcohol  (§  4,  p.  31)  for  forty-eight  hours,  stain  thick  sections 
with  resorcin-fuchsin  (p.  43)  and  mount  in  xylol-balsam  (Fig.  238). 

No.  131. — Blood-vessels  of  the  lungs. — Inject  the  lung  from  the 
pulmonary  artery  with  Berlin  blue  (p.  48);  fix  it  in  Miiller's  fluid,  and 
harden  it  in  alcohol.  Cut  thick  sections,  principally  parallel  to  the  sur- 
face of  the  lung  (Fig.  239). 

No.  132. — The  thyroid  gla^td. — Thin  sections  of  the  gland,  hard- 
ened in  toto  (see  No.  128),  are  to  be  stained  with  picrocarmine  (p.  41) 
and  mounted  in  xylol-balsam  (Fig.  240).      The  retracted  colloid  masses 


THE    URINARY    ORGANS.  321 

stain  an  intense  yellow.  Examine  thick  sections  in  glycerol,  in  which 
the  lymph-vessels  filled  with  colloid  substance  are  often  distinctly  visible. 
Vacuoles  in  the  colloid  are  artifacts  produced  by  fixation. 

No.  133. — TJic  thyiiuts. — Place  the  thymus  of  a  newborn  infant  in 
potassium-bichromate-acetic  acid  (p.  32)  and  harden  it  in  gradually 
strengthened  alcohols.  Stain  sections  with  Hansen's  hematoxylin; 
mount  them  in  xylol-balsam  (Fig.  241).  Care  should  be  taken  not  to 
confuse  the  cross-sections  of  the  blood-vessels,  the  lumina  of  which  when 
they  are  not  true  transverse  sections  change  in  elevating  and  depressing 
the  tube,  with  the  concentric  corpuscles  of  Hassal.  The  preparation 
represented  in  Fig.  242  is  from  a  thymus  fixed  in  Flemming's  mixture 
and  stained  with  safranin. 


VII.  THE   URINARY   ORGANS. 

The  Kidneys. 

The  kidneys  are  compound  tubular  glands,  which  consist  wholly 
of  minute  tubes,  the  urinifcroiis  tubules.  The  macroscopically  percep- 
tible differences  between  the  peripheral  and  the  central  portions  of  the 
organ,  the  so-called  cortical  and  medullary  regions,  are  principally  deter- 
mined by  the  course  of  the  uriniferous  tubules,  the  divisions  within  the 
cortex  pursuing  a  tortuous,  those  within  the  medulla  a  straight  course. 

Each  uriniferous  tubule  begins  in  the  cortex  as  a  spherical  dilatation 
enveloping  blood-vessels,  the  renal  corpuscle  (Malpighi,  Fig.  244),  which 
occasionally  is  marked  off  by  a  constriction,  the  neck,  from  the  greatly 
convoluted  succeeding  division,  the  convoluted  tulmle  (twhwlus  contortus), 
at  first  invariably  directed  corticalward.  This  passes  into  a  straight 
portion,  that  is  at  first  centrally  directed,  but  soon  turns  back  and  forms 
a  loop,  Henle's  loop,  in  which  a  thin  descending  and  a  thick  ascoiding  limb 
may  be  distinguished.*  The  latter  passes  into  a  shorter  convoluted 
portion,  the  intercalated  piece, ^  that  by  means  of  a  narrower  connect- 
ing piece  empties  into  a  collecting  tubule.  These  collecting  tubules  during 
their  centrally  directed  course  take  up  other  connecting  pieces,  farther 
on  unite  under  acute  angles  with  neighboring  collecting  tubules,  and  con- 
verge toward  the  apex  of  a  renal  papilla,  where,  diminished  in  number  but 
greatly  increased  in  diameter,  they  open  as  the  papillary  duct.  Henle's 
loop-tubules  and  the  collecting  tubules  are  named  straight  tubules  (tubuli 
recti).      Each    uriniferous  tubule   pursues  a  completely  isolated   course 

*  Since  the  transition  of  the  thin  into  the  thick  division  does  not  always  lie  at  the  curve 
of  the  loop,  the  designation  "  ascending  "  or  "descending  limb"  is  less  advisable. 

"f"The  intercalated  division  is  always  in  contact  with  the  renal  corpuscle  to  which  it 
belongs,  owing  to  the  mode  of  development  of  the  uriniferous  tubule  (Fig.  244). 

21 


322 


HISTOLOGY. 


until  it  is  taken  up  by  a  collecting  tubule.     The  loops  of  Henle  and  the 
peripheral  portions   of  the  collecting  tubules  are   grouped  together  in 


Renal  corpuscle 


Thin 
division.lof  the 
loop  of  Henle. 


Collectin 
tubule. 


Lobule. 


Lobule. 


Tunica  albuginea. 


Stellate  vein. 


Arciform    artery. 


Arciform  vein. 


—  -Literlobar  artery. 
.Interlobar  vein. 


Papillary  duct.  -*  > 


Fig.  244. — Scheme  of  the  Course  of  the  Uriniferous  Tubules  and  the  Renal  Vessels. 

bundles  as  they  pass  toward  the  medulla  and  form  the  structures  in  the 
cortex  known  as  the  medullary  rays  or  the  pyramids  of  Ferrcin. 

The  uriniferous  tubules  possess  in  their  entire  length  a  single-layered, 
single-rowed  epithelium,  but  their  minute  structure  differs  so  greatly  in  the 


THE    URINARY    ORGANS. 


323 


several  divisions  that  a  separate  consideration  of  each  division  is  necessary. 
The  renal  corpiisclc,  from  0.13  to  0.22  mm.  in  size,  consists  of  a  spherical 
plexus  of  blood-vessels,  the  glomeruhis,  and  the  expanded,  invaginated, 
blind  initial  piece  of  the  uriniferous  tubule,  the  capsule  of  the  gltvnenilus 
(Bowman).  The  glomerulus  lies  within  the  invaginated  portion  of  the 
capsule,  and  is  almost  completely  enveloped  by  it.  The  invagination  is 
similar  to  that  on  a  large  scale  of  the  heart  in  the  pericardium.     Accord- 


Proximal  convoluted  tubule.        Straight  collecting  tubule. 


Cortex. 


Renal  corpuscle. 


Medullary  ray. 


Medulla. 


\rciform  J 
\  ein. 


Running  at  the  bound- 
ary between  cortex 
and  medulla  (f/. 
longitudinal  aspect, 
Fig.  244). 


Blood-vessels. 


Henle's  loop. 


Fig.  245. — From  a  Section  of  Human  Kjdney  Including  a  Portion  of  the  Cortex  and  the  ]Medulla.    At 
X  two  renal  corpuscles  have  fallen  out      X  20      Techruc  No.  135. 

ingly  two  layers  are  distinguished  in  the  capsule,  an  inner  (quasi  visceral) 
lying  close  upon  the  glomerulus,  which  in  young  animals  consists  of 
cubical  cells,  that  later  become  more  and  more  flattened  and  fuse  into  a 
syncytium  (p.  73),  and  an  outer  (quasi  parietal)  layer,  that  is  composed 
of  flat,  polygonal  cells  (Fig.  246).* 

At  the  neck  the  outer  layer  of  the  capsule  passes  over  into  the  wall 
of  the  co7ivoluted  tuhilc,  which  is  from  40  to  60  fi  thick.  The  protoplasm 
of  the  cells  of  this  division,  the  boundaries  of  which  are  not  sharply 
defined,  consists  of  granules  that  by  means  of  protoplasmic  filaments  are 
bound  together  in  rows  radially  placed  to  the  lumen  ;  these  rows  are 
most  distinctly  seen  at  the  outer  end  or  base  of  the  cell  and  with  medium 


*  The  network  of  terminal   bars   (p.  79),  occurring    in    all  divisions    of  the   uriniferous 
tubules,  has  not  yet  been  successfully  demonstrated  on  the  epithelium  of  the  capsule. 


324 


HISTOLOGY. 


Outer 


Inner  leaf  (syncytium' 
of  the  capsule  of  thi 
glomerulus. 


magnification  have  the  appearance  of  minute  rods  (Fig.  247).     The  nu- 
cleus of  the  cells  always  lies  near  the  base  ;  the  surface  of  the  cells  di- 
rected toward  the  lumen 

Interlobular  artery.        Afferent  vessel.  Efferent  vessel.  -^   provided    with    an    ex- 

tremely unstable  striated 
border  (p.  76,  remark  *), 
the  "brush-border."* 
The  descending  liinb{\}c{\Vi 
division)  of  Henle's  loop 
is  from  9  to  1 5  p.  thick  ; 
the  lumen  is  very  wide. 
The  epithelial  cells  are 
flat  elements,  the  nuclei 
of  which  often  protrude 
into  the  lumen  (Fig.  249, 
i).  The  ascending  limb 
(thick  division)  is  from  23 
to  28  fx  thick,  the  lumen 
is  relatively  narrower.  The  epithelial  cells  resemble  those  of  the  convo- 
luted division,  but  are  somewhat  lower  (Fig.  249,  2).  The  transition  ot 
the  narrow  descending  limb  into  the  thicker  ascending  portion  does  not 
always  occur  at  the  curve  of  the  loop.  The  intercalated  portions  are  from 
39  to  44//.  thick;  their  epithelial  cells  are  cylindrical  or  conical  in  shape 
and  have  a  peculiar  luster  ;  here,  too,  rods  have  been  described.  The 
connecting  tiibides  are  about  25  //.  thick  and  are  clothed  with  a  cubical 
epithelium  similar  to  that  of  the  smallest  collecting  tubules.  The  collect- 
ing tiibides  increase  in  thickness  as  they  approach  the  apex  of  the  papilla  ; 
the  thinnest  have  a  diameter  of  45  //,  the  thickest,  the  papillary  ducts 
(ductus  papillares),  a  diameter  of  from  200  to  300  //.  Their  epitheHal 
cells  are  in  part  clear,  in  part  dark  cyHnder  elements  (Fig.  249,  3),  that 
increase  in  height  with  the  increase  of  the  caliber  of  the  tubule. 

The  renal  corpuscles  let  the  urine  water  pass  through,  the  rodded  epithelial 
cells  furnish  the  pigment  and  the  uric  acid  ;  the  thin  division  of  Henle's  loop, 
the  connecting  piece,  and  the  collecting  tubules  are  simply  excretory  canals. 


Glomerulus. 
Fig.  246. — Scheme  of  a  Renal  Corpuscle. 


*  According  to  recent  investigations  undertaken  on  winter  hibernating  animals  the  epi- 
thelial cells  of  the  convoluted  tubules  at  the  beginning  of  secretion  enlarge,  in  place  of  the 
brush-border  a  clear,  homogeneous  crest  appears  (Fig.  247  X),  while  the  granular  protoplasm 
with  the  nucleus  lies  at  the  cell  base.  Then  the  crest  empties  its  contents,  whereby  the  cell  be- 
comes smaller  and  the  lumen  of  the  tubule  wider.  After  a  period  of  rest  the  cells  again  become 
tall  (consequently  the  lumen  of  the  tubule  appears  narrow),  develop  a  brush-border,  and  up  to 
the  beginning  of  the  next  secretion  are  wholly  granular. 


THE    URINARY    ORGANS. 


325 


The  capsule  of  the  glomerukis   and  the  uriniferous  tubule  are  cov- 
ered in  their  entire  length  with  a  structureless  membrana  propria  situated 


Brush-border. 


Outer    leaf     of    the 
glomerulus  capsule. 


Rods. 


'^    Intercalated  tubule. 


X  (c/.    remark  *,    p. 
324)- 


J3fe».    Membrana  propria. 


Surface  section  of  an 
intercalated  tubule. 


■~~jr^-     Colored  blood-cells. 


Fig.  247. — From  a  Section  of  a  Human  Kidney.     X  240.     The  epithelium  covering  the  glomerulus  (i.  e.,  the 
inner  leaf  of  the  capsule)  cannot  be  distinctly  seen.     Technic  No.  135. 


outside  of  the  epithelium,  which  is  thickest  in  the  descending  limb  of 

Henle's  loop  and   gradually  disappears  toward 
/--.,_  the  papillary  duct.     The  tubules  are  enveloped 

'*/©*       f  aV^  in  a  small  amount  of  loose  connec- 

.d^         "^^'a,  .^  .         .  .  .  .    ,  .         . 

-?!        ®'8     I'i*  ».  XxvQ.  Xxs'iM^,  interstitial  connective  tis- 

A^'  -  -^     &  :g     J^^^.  Collecting  tubule.  ' 

■  '^;*V^'*«4  J®    «/  •^^^^>  which  on   the  surface 

h^*^^  :/«*  _#^ Tu;^  K  °^  ^^^  kidney  is  condensed 


[ft  ®, 


limb  of  a  loop-tubule  of 
Henle. 


Surface  view  of  a  thick  limb. 


Fig.  248. — Tubules  of  a  Medull.\ry  Ray.  From  a  Longi- 
tudinal Section  of  a  Human  Kidney.  X  240.  Tech- 
nic No.  135. 

to  a  fibrous  membrane,  the  tunica  albu- 

ginea,    containing    smooth    muscle-fibers 

and  elastic  fibers,  which  increase  in  old  age. 

stitial  connective  tissue,  which  is  relatively  poor  in  elastic  fibers. 


Fig.  249. — From  a  Cross-section  of  the 
Medulla  of  a  Human  Kidney. 
X  240.  The  section  is  through  the 
base  of  the  papilla,  i,  Thin,  2,  thick 
di\-ision  of  Henle's  loop.  3.  Collect- 
ing tubule.  4,  Blood-vessels  filled  with 
blood-cells.     Technic  No.  135. 


The  vessels  run  in  the  inter- 


Capsule  of  the 
glomerulus 
\ 


Intercalated . 
tubule. 


Convoluted  tubule. 


Capillary. 


Henle's  tubule.  / 

Small  collecting  tubule. 


Fig.  250. — From  a  Section  through  the  Cortex  of  a  Human  Kidney  (parallel  to  the  surface).    At  the  left 
lower  comer  there  is  a  cross-sectioned  medullary  ray.     X  200.     (Schaper.)     Technic  No.  135. 


Large  collecting  tubule 


Capmary.  "     ^;^'    .^    '.        ^      ;_  ^^    ^  ®l«y  ^^ 


'^^^ Ascending    limb 

"^  of  Henle's  loop. 


(  - 


f^ 


--  Descending  limb 
of  Henle's  loop. 


miH^ 


Fig.  251. — From  a  Transverse  Section 


THROUGH  the  Medulla  OF  A  HuMAN  KiDNEY.     X  320.     (Schaper.) 
Technic  No.  135. 


THE    URINARY    ORGANS. 


1^7 


The  blood-vessels  of  the  kidneys.  The  renal  artery  divides  in  the 
hilus  of  the  kidney  into  branches,  which  after  giving  off  small  twigs  to 
the  fibrous  capsule  and  the  tunica  albuginea,  and  to  the  renal  calices 
enter  the  parenchyma  of  the  organ  at  the  circumference  of  the  papillae 
and  as  the  interlobar  arteries  (arteriae  interlobares)  pass  without  branch- 
ing to  the  boundary  between  the  cortex  and  the  medulla  (Fig.  244). 
Here  the  arteries  bend  at  right  angles  and  form  very  irregularly  curved 
arches  {arteries  areifonnes)  along  the  boundary  line,  with  the  convexity 
toward  the  periphery.  From  the  convex  side  of  the  arches  and  from 
their  terminal  ramifications  branches  spring  at  regular  intervals,  that  run 
toward  the  periphery,  the  interlobidar  arteries  *  (arteriae  interlobulares) 
(Fig.  244,  252),  which  give  off  short  lateral  twigs,  each  of  which  sup- 
plies a  glomerulus  (Fig.  244,^). 
Each  interlobular  artery  breaks 
up  into  terminal  branches,  of 
which  some  supply  the  tunica 
albuginea,  some  continue  as  the 
capillaries  of  the  cortex  or  form 
the  afferent  vessel  of  a  glomeru- 
lus. Each  glomerulus  arises  by 
the  rapid  division  ot  an  artery 
into  a  number  of  small  capillary 
twigs, t  that  immediately  reunite 
in  a  single  (arterial)  vessel ;  % 
this  latter  is  called  the  efferent 
artery  (Fig.  244  c,  252) ;  it  is 
somewhat  smaller  than  the  en- 
tering vessel  of  the  glomerulus, 
which  is  called  the  afferent  artery 
(Fig.  244  a,  252).  The  efferent 
artery  breaks  up  into  a  capillary 
network,  with  elliptical  meshes   in  the  region  of   the    medullary  rays, 


Capillary  network  of 
cortex  vrith  round 
meshes. 

Interlobular  vein. 
Interlobular  artery. 


Afferent  vessel. 
Efferent  vessel. 

Capillary  network  of 
a  medullary  ray  with 

elliptical  meshes " 


Fig.  252. — From  a  Longitudinal  Section  of  the  In- 
jected KiDN-EY  OF  A  Guinea-pig.  X  30.  Technic 
No.  137- 


*  Microscopic  regions  of  the  kidney  with  ill-defined  boundaries,  in  the  axis  of  which  lies 
a  medullary  ray  and  at  the  periphery  of  which  interlobular  arteries  ascend,  are  designated  lob- 
ules. In  Fig.  244  two  lobules  are  indicated.  These  lobules  have  no  relation  whatever  to  the 
lobules  of  the  kidney  during  fetal  life. 

j  The  wall  of  these  capillaries  is  said  to  consist  of  a  common  protoplasmic  mass  without 
nuclei ;  possibly  the  syncytium  of  the  inner  lamella  of  the  capsule  (p.  323)  contains  elements 
of  the  vascular  wall. 

X  Consequently  each  glomerulus  is  an  arterial  rete  mirabile  ip.  143,  remark*).  In  dogs 
and  cats  retia  mirabilia  occur  in  the  kidneys  that  do  not  stand  in  any  relation  to  uriniferous 
tubules,  that  is,  they  are  not  enveloped  in  a  "  capsule." 


328 


HISTOLOGY. 


with  round  meshes  in  the  region  of  the  convoluted  tubules.  From  the 
latter  veins  arise,  the  inter'lobular  veins  (vense  interlobulares)  (Fig.  244, 
252),  which  lie  close  beside  the  interlobular  arteries,  in  their  further 
course  continue  alongside  the  arteries,  and  open  into  the  vense  arci- 
formes  ;  the  latter  also  take  up  small  veins  that  arise  from  the  con- 
fluence of  capillaries  situated  in  the  deeper  portions  of  the  cortex.  The 
veins  of  the  peripheral  zone  of  the  cortex  converge  to  points  where 
they  unite  in  radicles  arranged  in  a  stellate  form,  the  venm  stellatcB  (Ver- 
heynii),  which  are  connected  with  the  interlobular  veins.  The  foregoing 
account  of  the  distribution  of  the  blood-vessels  appHes  only  to  the  cortex 
and  to  the  medullary  rays. 

The  medulla  receives  its  blood  supply  from  (i)  the  arterioles  rectce, 
which  arise  partly  from  the  efferent  vessels  of  the  most  deeply  situ- 
ated ,  (in  animals  relatively  large)  glomeruH  (Fig.  244,  4  and  252), 
and  partly  direct  from  centrally  running  branches  of  the  interlobular 
arteries  or  of  the  arciform  arteries  (Fig.  244,  3,  2);  and  (2)  from  off- 
shoots of  the  cortical  capillaries  (Fig.  244,  i).  The  veins  of  the  medulla 
take  their  origin  from  the  wide-meshed  capillary  network  surrounding 
the  papillary  ducts  and  empty  in  the  vense  arciformes.  The  renal  vein 
and  its  branches  have  no  valves.  Direct  communication  between  the 
arteries  and  the  veins  occurs  both  in  the  tunica  albuginea  and  in  the  in- 
terior of  the  kidney. 

The  lymph-vessels  originate  from  a  rietwork  of  closed  capillaries 
occurring  in  the  cortex  (a  similar  network  ap- 
pears to  be  present  in  the  medulla) ;  the  small 
trunks  arising  from  them  run  with  the  blood- 
vessels, without  enveloping  them  (p.  136),  and 
make  their  exit  at  the  hilus.  Besides  these  deep 
lymph-vessels  there  are  two  superficial  capillary 
nets,  one  in  the  capsula  adiposa  and  one  in  the 
capsula  fibrosa  (the  latter  is  in  communication 
with  the  cortical  capillary  plexus).  The  small 
trunks  originating  from  them  empty  into  neigh- 
boring lymph-glands. 

The  partly  medullated  nerves  run  either 
with  the  blood-  and  lymph-vessels  in  the  con- 
nective-tissue capsule  of  the  kidney  or  they  form 
in  the  hilus  a  plexus  intermingled  with  sympa- 
thetic nerve-cells,  in  the  construction  of  which 
the  branches  supplying  the  renal  pelvis,  as  well  as  the  nerves  that  ac- 
company the  blood-vessels  participate.      In  the  interior  of  the  kidney  the 


Renal 


Silvered  uriniferous 
tubule. 

Fig.  2S3. — Section  of  the  Kid- 
ney OF  A  Mouse.  X  i8o. 
Technic  No.  138. 


THE    URINARY    ORGANS. 


329 


nerves  form  networks  which  envelop  the  arteries  up  to  the  renal  cor- 
puscle (Fig.  253).  The  walls  of  the  veins  and  the  capillaries  are  also 
encircled  by  nerve  networks,  delicate  branches  of  which  form  epilemmal 
and  hypolemmal  networks  (p.  247)  on  the  straight  and  particularly  on 
the  convoluted  uriniferous  tubules,  from  which  delicate  interepithelial- 
endincf  nerve  filaments  arise. 


Fibrous  mem- 
brane. 


'*(  Muscular 
mem- 
brane. 


The   Urinary  Passages. 

The  caliccs  and  pelvis  of  the  kidney  and  the  ureter  consist  of  three 
membranes:  innermost  lies  (i)  the  mucous  membrane,  then  follows  (2) 
the  muscle  membrane, 
which  is  enveloped  in 
(3)  the   fibrous   mem- 
brane (Fig.  254). 

The  constituent 
parts  of  the  mucous 
membrane  are  {ci)  an 
epithelium  that  in  sec- 
tions exactly  resem- 
bles the  epithelium  of 
a  moderately  con- 
tracted urinary  blad- 
der* (p.  330);  {b)  a 
tunica  propria,  which 
consists  of  delicate 
connective -tissue 
fibers,  a  very  few 
elastic   fibers,  and 

many  cellular  elements  (leucocytes  also  are  occasionally  found  here),  and 
passes  without  sharp  boundaries  into  the  similarly  constructed,  but  loose 
submucosa. 

The  muscle  membrane  is  not,  like  that  of  the  wall  ot  the  intestine, 
formed  of  a  closed  layer,  but  is  frequently  interrupted  by  connective 
tissue  ;  an  inner  longitudinal  (/)  and  an  outer  circular  layer  (r)  of  smooth 
muscle-fibers  can  be  distinguished,  which  latter  in  the  lower  half  of  the 
ureter  is  covered  with  longitudinally  disposed  strands  of  muscle  (/i).t 
The  so-called  "  wall-piece  "   of  the  ureter,  running  in   the  wall  of  the 

*The  isolated  epithelial  cells  of  the  calices,  the  pelves,  and  the  ureters  also  cannot  be 
distinguished  from  those  of  the  urinary  bladder. 

f  The  lowermost  division  of  this  layer,  about  5  cm.  long,  is  particularly  thick  and  is 
described  as  the  ureteral  sheath. 


Fig.  254. — Transverse  Section  of  the  Lower    Half   of  a    Human 

Ureter.  X  15.  e,  Epithelium  ;  t,  tunica  propria  ;  s,  submucosa  ;  /, 
inner  longitudinal  muscle-bundles  ;  r,  circular  layer  of  muscle-bundles  ; 
/i,  accessory  outer  longitudinal  muscle-bundles.     Technic  No.  139. 


330  HISTOLOGY. 

urinary  bladder,  possesses  only  longitudinal  muscles,  that  are  not  con- 
nected with  the  muscles  of  the  latter,  but  end  free  in  the  tunica  propria  of 
the  vesical  mucous  membrane.  Their  contraction  opens  the  mouth  of  the 
ureters. 

The  fibrous  membrane  (tunica  adventitia)  consists  of  loose  connec- 
tive-tissue bundles  and  elastic  fibers. 

The  mucous  membrane  of  the  renal  calices  continues  over  the  surface 
of  the  renal  papillae  ;  the  circular  muscle-fibers  form  a  ring  muscle  round 
the  papillae. 

The  blood-  and  lynipli-vessels  are  especially  rich  in  the  mucous  mem- 
brane ;  the  blood  capillaries  situated  immediately  beneath  the  epithelium 
occasionally   project    toward    the    latter   and,    particularly   in   the  renal 


Cylinder  cells 

with  a  cuticu- 
.  lar  border. 


—  Tunica  propria. 


Fig.  255. — Portion  of  a  Vertical  Section  of  a  Human  Vesical  Mucous  Membrane.     X  560.    Technic 

No.  140. 

pelves,  counterfeit  "  intraepithelial  blood-vessels."  The  nerves  are  partly 
motor — they  are  distributed  in  the  muscles — and  partly  sensory — they 
form  bush-like  endings  in  the  tunica  propria  or  they  terminate  free  be- 
tween the  epithelial  cells. 

The  urinary  bladdcr\\k&w\sc  consists  of  a  mucous  membrane,  a  muscle 
membrane,  and  a  fibrous  membrane.  The  epithelium  of  the  contracted 
or  moderately  filled  organ,  in  vertical  sections  (Fig.  255),  resembles  strati- 
fied squamous  epithelium  ;  but  with  this  difference,  that  the  cells  of  the 
superficial  stratum  are  cylindric  or  cubical  elements  or  thick  plates. 
Uncertain  whether  to  class  this  epithelium  with  the  stratified  squamous 
or  the  stratified  cylinder  epithelium,  it  has  been  named  tra7isitional  epi- 
tJielhnn. 

It  has  been  demonstrated  by  careful  investigations  that  in  reality  only  two 
strata  are  present,  the  form  of  which  varies  extraordinarily  according  to  the 
content  of  the  bladder.     In  the  empty,  strongly  contracted  organ  the  cells  of 


THE    URINARY    ORGANS.  33  I 

the  superficial  stratum  are  cubical,  cylindrical,  and  on  their  under  surface  often 
provided  with  depressions  and  processes,  to  which  the  cells  of  the  deeper  stra- 
tum are  attached.  The  latter  are  slender  elements,  expanded  in  the  vicinity 
of  the  nucleus;  the  usually  simple  nucleus  lies  sometimes  at  the  upper  end, 
sometimes  at  the  lower  end,  sometimes  in  the  middle  of  the  cell.  This  gives 
rise  in  sections  to  the  false  appearance  of  a  stratified  epithelium.  In  the 
completely  filled  bladder  the  superficial  cells  are  quite  flattened,  the  deep  cells 
are  low,  cubical,  and  their  transverse-oval  nuclei  lie  in  a  single  row.  Between 
these  two  extremes  many  transitions  exist. 

With  the  proof  that  the  epithelium  of  the  bladder  is  in  reality  two-lavered, 
the  familiar  fact  that  the  terminal  bars  form  networks,  not  only  on  the  sur- 

Tangential  sections 
Crypt.  of  crypts.  Secretion.  Gland. 


-v>-; 


^u:^: 


Tunica  propria.  Smooth  muscles. 

Fig.  256. — Section  through  the  Fundus  of  the   Urixary  Bladder  of  Adult  Man.     X  48.     Technic 

Xo.  140. 

face  but  also  in  the  depths,  is  satisfactorily  explained  :    this  occurs  only  in  the 
contracted  organ  ;   in  the  expanded  organ  the  network  lies  on  the  surface. 

Granules  can  often  be  demonstrated  in  the  epithelial  cells,  particularly  in 
those  of  the  superficial  stratum,  that  possibly  are  precursors  of  secretion.  These 
cells  of  the  upper  stratum  are  further  distinguished  by  the  deeper  staining  of 
their  protoplasm,  by  the  occasional  presence  of  a  cuticular  border  (Fig.  255), 
as  well  as  by  the  frequent  possession  of  several  nuclei  that  have  arisen  by 
amitosis. 

In  the  superficial  strata  of  the  tunica  propria  (also  in  the  lower 
division  of  the  renal  pelvis  and  the  upper  division  of  the  ureter)  round  or 
oblong  bodies  are  found  :  sprouts  of  the  superficial  epithelium,  in  part 


332  HISTOLOGY. 

without  a  lumen  ;  *  little  strands,  partly  hollow  ;  crypts,  the  lumen  of 
which  contains  secretion,  a  colloid  substance.  These  structures  are  the 
initial  stages  in  the  development  of  glands,  that  do  not  until  in  adult 
life  grow  from  the  base  of  the  crypt  and  develop  into  branched  follicles 
clothed  with  cylinder  epithelium. 

Such  true  glands  occur  only  in  the  urinary  bladder,  at  the  fundus, 
the  trigonum,  and  the  beginning  of  the  urethra,  where  they  exhibit  all 
transitions  to  well-developed  prostate  glands  (p.  345).  The  tunica 
propria,  which  blends  insensibly  with  the  submucosa,  occasionally  con- 
tains solitary  lymph  nodules.  The  muscle  stratum  consists  of  smooth 
muscle-fibers,  an  inner  and  an  outer  longitudinal  layer,  which  enclose 
between  them  a  circular  layer.  The  layers  are  interlaced  with  one  an- 
other in  such  a  manner  that  a  sharp  demarcation  of  the  same  is  not  pos- 
sible. At  the  base  of  the  bladder  the  inner  longitudinal  muscle-layer  is 
strengthened  and  at  the  beginning  of  the  urethra  the  ring  muscle-layer 
forms  the  not  always  distinct  internal  vesical  sphincter. 

The  blood-  and  lymph-vessels, f  as  well  as  the  nerves,  provided 
with  small  groups  of  ganglion  cells,  behave  as  in  the  ureter. 

The  female  urethra  consists  of  a  mucous  membrane  and  a  powerful 
muscular  membrane.  The  tunica  propria  mucosae  is  composed  of  a  fine- 
fibered  connective  tissue,  richly  interspersed  with  cells,  that  on  its  sur- 
face is  elevated  in  numerous  papillae,  especially  well  developed  on 
the  external  meatus.  The  epithelium  varies  individually,  is  sometimes 
stratified  squamous  epithelium,  more  often  simple  cylinder  epithelium. 
A  few  branched  simple  tubular  glands  are  present;  they  occur  in  small 
groups  at  the  meatus  and  are  called  "  periurethral  "  glands.  The  mus- 
cular membrane  consists  of  an  inner  longitudinal  and  an  outer  circular 
layer  of  smooth  muscle-fibers,  between  which  extends  a  compact  con- 
nective tissue  mixed  with  many  elastic  fibers.  The  mucous  membrane 
is  rich  in  venous  blood-vessels,  the  networks  of  which  extend  into  the 
longitudinal  layer  of  the  muscular  membrane ;  in  this  way  a  structure 
similar  to  the  corpus  cavernosum  of  the  male  urethra,  the  corpus  spongi- 
osum, is  formed. 

The  viale  urethra  (better,  "  male  urogenital  sinus  ")  like  that  of  the 
female  consists  of  a  mucous  membrane  and  a  muscular  membrane,  but  it 
differs  in  structure  in  the  different  divisions  of  the  canal.  In  the  prostatic 
portion  the  epithelium   resembles  that  of  the  urinary    bladder;    in    the 

*  Occasionally  the  connection  with  the  superficial  epithelium  appears  to  have  been  lost. 

f  Not  only  the  muscular  membrane,  but  also  the  mucous  membrane  of  the  urinary  bladder 
contains  a  lymph-vessel  plexus,  that  in  the  lower  division  of  the  organ  is  especially  well 
developed. 


THE    URINARY    ORGANS.  333 

membranous  division  it  gradually  passes  into  a  stratified  cylinder  epithe- 
lium, which  finally  in  the  cavernous  part  is  transformed  to  a  simple 
cylinder  epithelium.  From  the  fossa  navicularis  on  the  epithelium  is  of 
the  stratified  squamous  type.  The  tunica  propria  is  rich  in  elastic  fibers 
and  is  beset  with  papillae,  that  are  especially  well  developed  in  the  fossa 
navicularis.  Isolated,  branched,  alveolo-tubular  simple  glands,  the 
urethral  glands  {^glandiilcE  urethralcs)  (Litrii),  occur  throughout  the  entire 
urethra  (Fig.  269).  Transition  forms  occur  between  these  glands  and 
the  evaginations  of  the  mucous  membrane,  the  "  lacunae,"  clothed  with 
a  simple  cylinder  epithelium.  The  muscular  membrane  in  the  prostatic 
division  consists  of  an  inner  longitudinal  and  an  outer  circular  layer  of 
smooth  muscle-fibers  ;  both  layers  are  still  well  developed  in  the  mem- 
branous portion,  but  gradually  cease  in  the  cavernous  portion,  where  the 
circular  layer,  still  conspicuous  in  the  bulbus  urethrae,  is  the  first  to  dis- 
appear ;  in  the  anterior  part  of  the  cavernous  division  only  a  few  oblique 
and  longitudinal  bundles  occur.  The  mucous  membrane  of  the  male 
urethra  has  a  rich  vascular  supply  (see  corpus  cavernosum  urethrae,  p. 
347).  The  lymph-vessels  lie  beneath  the  blood-vessels.  The  nerves 
form  networks  intermixed  with  nerve-cells  ;  the  nonmedullated  fibers 
arising  from  them  terminate  partly  in  free  endings,  partly  (in  the  prostatic 
and  the  membranous  portion)  in  special  end  apparatus  {cf.  p.  224). 

TECHNIC. 

No.  134. — Isolated  iiriniferoiis  Uibidcs. — The  most  suitable  for  this 
preparation  are  the  kidneys  of  young  animals,  for  example  newborn  kittens. 
Divide  the  kidney  in  halves  ;  place  one  half  {a)  aside  for  investigation 
fresh  ;  cut  the  other  half  {U)  into  pieces  including  cortex  and  medulla,  and 
place  them  in  30  c.c.  of  pure  hydrochloric  acid. 

{a)  Tease  a  pea-sized  piece  in  a  drop  of  0.75  per  cent,  salt  solution. 
The  red  glomeruli,  the  convoluted  and  straight  uriniferous  tubules,  can 
be  seen  with  the  low  power.  The  convoluted  tubules  are  dark  and 
granular,  the  other  divisions  clear.  With  high  magnification  the  nuclei 
of  the  clear  portion  of  the  uriniferous  tubules  can  be  distinctly  perceived  ; 
the  cell  boundaries  can  best  be  seen  in  the  collecting  tubules.  In  the 
convoluted  tubules  only  the  fine  striation  of  the  base  of  the  gland-cells 
can  be  seen  ;  cell  boundaries  and  nuclei  are  not  visible. 

{b)  In  about  two  hours  the  red  pieces  of  kidney  tissue  should  be 
transferred  to  a  capsule  containing  50  c.c.  of  distilled  water,  in  which 
they  rapidly  become  a  dull  gray,  with  smeary  surfaces.  The  water  is  to 
be  changed.  After  a  few  moments  small  pieces  can  be  detached  with 
needles  and  readily  separated  into  tubules,  in  a  little  water  on  a  slide.  If 
it  is  desired  to  obtain  entire  uriniferous  tubules  transfer  pieces  of  kidney 
2  mm.  square  to  a  watch-glass  in  which  has  been  placed  a  large  cover- 


334 


HISTOLOGY. 


glass  and  enough  distilled  water  to  cover  the  surface  of  the  latter.      The 
attempt  should  now  be  made  to  isolate  the  tubules  with  needles.      If  the 

isolation  is  successful — this  may  be  ascer- 
tained by  examination  with  the  low  power 
— with  a  pipet  or  filter-paper  carefully  ab- 
sorb the  water  from  the  watch-glass  and 
then  from  the  cover-glass,  take  out  the 
latter,  cleanse  its  free  surface,  and  place  it 
with  the  attached  tubules  gently  on  a  slide 
on  which  a  drop  of  dilute  glycerol  has  been 
previously  placed.  The  preparation  may 
be  subsequently  stained  under  the  cover- 
glass  with  picrocarmine  (Fig.  257). 

No.  135. — The  cortex  and  the  medulla 
of  the  kidney. — For  sections  the  kitten's 
other  kidney  or  pieces  of  another  kidney  2 
or  3  cm.  square  are  to  be  fixed  in  200  or 
300  c.c.  of  Miiller's  fluid  for  four  weeks 
(p.  33),  and  hardened  in  100  c.c.  of  gradu- 
ally strengthened  alcohols  (p.  35).  Thick 
transverse  and  longitudinal  sections  through 
the  cortex  and  similar  ones  through  the  me- 
dulla are  to  be  examined  unstained  in  dilute 
glycerol,  with  a  low  power.  Thin  trans- 
verse sections  [a)  through  the  apex  of  the 
papillae  for  the  papillary  duct,  (^)  through 
the  base  of  the  papillje  (Fig.  249),  and  {c) 
transversely  and  longitudinally  through 
the  cortex  are  to  be  stained  with  Hansen's 
hematoxylin  (p.  38)  and  mounted  in  xylol- 
balsam.  The  extremely  delicate  "brush- 
borders  "  can  be  seen  only  in  very  thin  sec- 
tions.     Frequently  they  have  fallen  off 

Endeavor  to  cut  radial  sections  through 
the  cortex  and  the  medulla,  showing  the 
boundary  between  the  two  ;  examine  them 

unstained  in  glycerol,  with  the  low  power.      Frequently  the  blood-vessels 

are  still  filled  with  blood  corpuscles  and  can  be  traced  for  long  distances. 
For  the  study  of  the  glomerulus  and  its  capsule,  also  the  connection 

of  the  latter  with  the   uriniferous  tubule,  very  thin   microtome   sections 

must  be  made  (Figs.  247,  250). 

No.  136. — Medullary  rays  and  Henle's  loops  are  especially  fine  in 
stained  vertical  sections  of  the  kidneys  of  young  animals  prepared  after 
No.  135. 

No.  137. — Blood-vessels  of  the  kidney. — An  isolated  kidney  can  be 
injected  (p.  48),  fixed  in  300  c.c.  of  Miiller's  fluid  (p.  33)  for  four  weeks 


/ 


Fig.  257. — Isolated  Uriniferous  Tu- 
bules OF  A  Four-Week-Old  Rab- 
bit. X  30.  a.  Renal  corpuscle,  b. 
Convoluted  tubule.  c,  Henle's  loop, 
descending  limb  ;  d,  ascending  Hmb. 
/,  Collecting  tubule,  g.  Papillary  duct. 


THE    URINARY    ORGANS.  335 

and  then  hardened  in  150  c.c.  of  gradualh'  strengthened  alcohols  (p.  35). 
The  surface  aspect  of  the  venae  stellatae  should  be  examined  macroscop- 
ically.  Unstained  thick  longitudinal  and  transverse  sections  should  be 
studied  with  the  low  power  (Fig.  252). 

No.  138. — Xcrvcs  of  tlic  kidney. — Treat  small  pieces  according  to 
Golgi's  method,  given  on  p.  45  ;  they  should  remain  from  three  to  six 
days  in  the  osmiobichromate  mixture.      Result:   Fig.  253. 

No.  139. —  TJie  renal  pelvis  eaid  the  iireters. — Of  the  former  pieces  i 
cm.  square,  of  the  latter  i  or  2  cm.  long,  should  be  fixed  in  100  c.c.  of 
IMiiller's  fluid  (p.  33)  and  in  fourteen  days  hardened  in  100  c.c.  ot 
gradually  strengthened  alcohols  (p.  35).  Stain  sections  with  Hansen's 
hematox)lin  (p.  38)  and  mount  in  xylol-balsam. 

No.  140. — Treat  the  bladder  after  No.  139. 

No.  141. — EpitJielial  cells  of  tlic  renal  pelvis,  of  tJie  iireter,  and  of  the 
bladder. — Treat  pieces  of  each  i  cm.  square  (cut  open  the  ureter),  with 
30  c.c.  of  Ranvier's  alcohol  (p.  29).  Isolate  and  stain  with  picrocarmine 
(P-  53)-      Blount  in  diluted  acidulated  glycerol. 

No.  142.  Tlie  female  Jirethra. — Cut  out  a  piece  about  2  cm.  long 
of  the  female  urethra,  together  with  the  attached  anterior  vaginal 
wall ;  place  it  in  100  or  200  c.c.  of  Miiller's  fluid  (p.  33)  for  fixation  and 
in  two  or  three  weeks  harden  it  in  gradually  strengthened  alcohols  (p. 
35).  Stain  cross-sections  in  Hansen's  hematoxylin  (p.  38)  and  mount  in 
xylol-balsam. 

No.  143. —  The  male  urethra. — Treat  pieces  i  or  2  cm.  long  of  the 
prostatic,  membranous,  and  cavernous  portions  and  of  the  fossa  navic- 
ularis  after  No.  142.  Care  should  be  exercised  not  to  confuse  the 
urethral  lacunae  (Morgagni),  blind  evaginations  of  the  mucosa,  with 
sections  of  elands. 


336 


HISTOLOGY. 


VIII.     THE    REPRODUCTIVE    ORGANS. 

THE  MALE    REPRODUCTIVE   ORGANS. 

The   Testes. 

The  testes  are  glands  consisting  of  branched,  pouch-Hke  tubules, 
the  seminiferous  tubules,  which  are  enveloped  in  a  connective-tissue  cap- 
sule. This  capsule,  the  tunica  albuginea  s.  fibrosa  (Fig.  258),  is  a  com- 
pact membrane,  which  encloses  the  parenchyma  on  all  sides  and  on  the 


Ductus  deferens. 
Blood-vessels. 

Epididymis. 


Mediastinum, 
containing  the 
rete  testis. 

■  Straight  tubules. 


/ 


Septa. 


;  Lobules,  consist- 
ing of  convo- 
luted tubules. 


.Tunica  vascu- 
losa. 

-Tunica  albu- 
ginea. 


Fig.  258. — Cross-section  of  the  Testis  of  a  Newborn  Child.     X  lo.    Technic  No.  144. 


posterior  upper  aspect  is  developed  into  a  mass,  the  mediastinum  testis 
{corpus  Highmori),  which  juts  into  the  interior  of  the  organ.  From 
this  a  number  of  septa  arise,  the  septula  testis,  which  pass  along  divergent 
paths  to  the  tunica  albuginea  and  thus  divide  the  parenchyma  of  the 
testis  into  pyramidal  lobides,  the  base  of  which  is  directed  toward  the 
capsule,  the  apex  toward  the  corpus  Highmori.  The  tunica  albuginea 
consists  of  dense  fibrous  connective  tissue  and  numerous  elastic  fibers, 
that  increase  with   the    years  ;   on   its   free   surface  it  is   covered  with  a 


THE    REPRODUCTIVE    ORGANS. 


337 


simple  layer  of  flat  epithelial  cells,*  on  its  inner  surface  it  is  in  contact 
with  a  layer  of  loose  connective  tissue  mixed  with  elastic  fibers  ;  this 
supports  numerous  vessels  and  is  called  the  tunica  vasciilosa ;  it  is 
connected  with  the  interlobular  septa.  The  mediastinum  is  con- 
structed of  dense  connective  tissue  and  numerous  elastic  fibers  and  en- 
closes in  its  interior  a  network  formed  of  freely  anastomosing  tubules,  the 
rcte  testis  (Halleri).  The  interlobular  septa  consist  of  bundles  of  con- 
nective tissue,  which  are  connected  with  the  loose  connective  tissue 
surrounding  the  individual  seminiferous  tubules.  This  "interstitial" 
connective  tissue  is  rich  in  cellular  elements,  which  are  in  part  flat 
connective-tissue  cells,  in  part  spherical  cells,  the  so-called  interstitial 
cells,  containing  pigment  or  fat  granules,  in  the  sexually  mature  testis, 
also  crystalloids  f  (Fig.  260  and  261). 

The  seminiferous  tubnles  in  their  course  may  be  divided   into  three 


Developing 
semen    fila- 
ments. 


Interstitial     con- 
nective tissue. 


Epithelium  in  a 
state  of  ac- 
ti\-ity. 


Epithelium  in   a 
state  of  rest. 


Fig.  259. — From  a  Cross-section  of  the  Testis  of  an  Ox.  X  so.  In  the  process  of  fixing  and  harden- 
ing the  epithehum  has  become  somewhat  shrunken,  so  that  spaces  exist  between  it  and  the  interstitial  con- 
nective tissue.     Technic  Xo.  145. 

portions  :  they  begin  as  (i)  the  convoluted  tubules  (tubuli  contorti),  which 
pass  into  (2)  the  straight  tubules  (tubuli  recti),  which  continue  as  (3)  the 
rete  testis.  The  convoluted  tubules  are  round,  serpentine  canals,  about 
140  n  in  diameter,  the  initial  extremity  of  which  has  not  yet  been  satisfac- 
torily oriented  ;  probably  they  are  freely  united  with  one  another  at  the 
periphery,  beneath  the  tunica  vasculosa,  and  form  a  network, [j;  from  which 
numerous  tubules  turn  aside  and  with  many  windings  pass  toward  the 
mediastinum.      During    their    course    the  tubules  diminish  in   number, 


*  This  is  the  visceral  layer  of  the  tunica  vaginalis  propria. 

f  Such  structures  are  more  common  in  the  vegetable  world,  but  have  recently  been 
found  in  other  animal  cells,  e.  g.  in  the  nuclei  and  the  protoplasm  of  the  nerve-cells  of  the  por- 
cupine and  in  the  protoplasm  of  the  lens  epithelium. 

j  Seminiferous  tubules  with  blind  ends  have  been  observed. 
22 


338 


HISTOLOGY. 


because  they  continually  unite  with  one  another  under  narrow  angles. 
Not  far  from  the  mediastinum  the  convoluted  tubules  pass  into  the 
straight  tubules  (Fig.  258)  which,  considerably  reduced  in  size  (20  to 
25  //  thick),  after  a  short  course  penetrate  into  the  mediastinum  and  form 
the  rate  testis,  the  tubules  of  which  measure  from  24  to  180  //. 


Interstitial  cells. 


Connective 
tissue. 


Convoluted 
'      lubules. 


Fig.  260. — From  a  Cross-section  of  the  Testis  of  a  Man  22  Years  Old.     X  so.     Technic  No.  145. 

The  wall  of  the  comwluted  Uibides  from  without  inward  consists  of 
(i)  several  layers  of  flattened  connective -tissue  cells  interlaced  with  many 
elastic  fibers,  (2)  a  thin  membrana  propria,  and  (3)  a  stratified  epithelium. 


Heads  of  semen 
filaments. 


Spermatocyte. 


Crystalloids  in    /  .i 
interstitial  cells,  c^rc 


'■^-'    '■.-,t-<il    ■-'    **■'     ^Spermatid. 


---.._ 

/z.    %  ^ 

-, 

$5.'    ^    • 

%  <^ 

x^%  ^ 

^1 

jX  »>^ .  ,^ 

;^    Xuclei    of    cells 
"^f"        of  Sertoli. 


Spermatogon- 
ium. 


Interstitial    con- 
nective tissue. 


Fig.  261. — From  a  Longitudinal  Section  through  a  Convoluted  Tubule  of  a  Human  Testis. 

X  360.     Technic  No.  145. 


the  appearance  of  which  differs  greatly  in  the  separate  divisions  of  the 
tubules. 

When  the  epithelium  is  in  a  state  of  rest  (as  well  in  the  immature 
testis,  as  in  individual  tubules  of  the  sexually  ripe  human  testis)  the 
tubules  appear  to  be  clothed  in  several  strata  of  spherical  cells,  the  nuclei 
of  which  stain    sometimes    more,   sometimes   less   intensely  (Fig.   260). 


THE    REPRODUCTIVE    ORGANS. 


339 


When  the  epithelium  is  in  a  state  of  activity  it  exhibits  a  series  of  pic- 
tures that  are  related  to  the  development  of  semen,  to  "  spermatogenesis." 
The  s,\.x2X\xvci,  parietal  stratum,  of  membraneless  epithelial  cells  lying  next 
to  the  membrana  propria  consists  of  two  kinds,  the  cells  of  Sertoli  (Fig. 
262),  which  take  no  direct  part  in  the  production  of  the  semen  filaments, 
and  the  spennatogonia  (ancestral  cells),  the  real  producers  of  the  semen. 
The  latter  multiply  by  indirect  division  and  grow  to  be  large  cells,  that 
occupy  the  next  layer   within.      These  are  the  spermatocytes  (mother- 


Blood-vessel  with 
blood  corpuscles. 


Spermatids. 


Sertoli's  cell. 


Spermatogonia,  above 
each  a  large  spermatocyte. 


Sertoli's  cells. 


Fig.  262. — Cross-section  of  Seminiferous  Tubules  of  a  Mouse.  X  360-  Observe  that  the  nuclei  of  the 
spermatids  (below  on  the  left),  at  tirst  round,  become  oval  (above)  and  are  transformed  (below  on  the  right) 
into  the  heads  of  the  semen  filaments.     Technic  No.  146. 

cells),  which  divide  twice,  each  giving  rise  to  four  smaller  cells,  the 
spermatids,  lying  in  a  zone  still  nearer  to  the  center  of  the  tubule.  The 
latter  now  become  spcrmatosomes  (semen  filaments),  by  the  nucleus  of 
each  spermatid  developing  into  the  head,  a  small  portion  of  the  proto- 
plasm forming  the  tail,  while  the  axial  fiber  (p.  341)  grows  out  of  the 
distal  centrosome  of  the  diplosome  (p.  6€)  lying  beneath  the  surface  of 
the  cell. 

The  cells  of  Sertoli  are  characterized  by  a  nucleus  poor  in  chromatin, 
containing  a  distinct  nucleolus,  as  well  as  by  a  protoplasm  provided  with 


340  HISTOLOGY. 

brownish  fat-granules.  In  animals  the  nucleus  usually  lies  on  a  level 
with  the  spermatogonia  (Fig.  262),  in  man  not  seldom  between  the  sper- 
matocytes (Fig.  261).  The  role  of  the  cells  of  Sertoli  is  generally  as- 
sumed to  be  sustentative  ;  it  is  supposed  that  during  the  processes  just 
described  a  large  number  of  spermatids  unite  with  a  cell  of  SertoH,* 
that  meanwhile  has  grown  in  length  centrad,  and  that  through  this 
plasma  union  ("copulation")  they  in  all'  probability  receive  nutritive 
material. 

Another,  but  much-disputed  theory  is  that  the  cells  of  Sertoli  likewise  are 
elements  produced  by  the  spermatogonia,  but  instead  of  developing  they  perish; 
their  protoplasm  gradually  passes  into  the  intercellular  substance  occurring  be- 
tween all  the  cells  and  there  dissolves  ;  their  nucleus  disappears.  The  tuft-like 
arrangement  of  the  semen  filaments  is  the  result  of  the  pressure  exercised  by 
the  spermatogonia  lying  about  the  cells  of  Sertoli. 

In  the  lumen  of  the  seminiferous  tubules  (also  in  the  epididymis)  round, 
often  multinucleated  cells  are  found  beside  developed  semen  cells  ;  they  are 
spermatocytes  that  have  not  completed  their  development  and  are  perishing. 

The  ticbiili  recti  and  the  canals  of  the  retc  testis  are  clothed  with  a 
simple  layer  of  cubical  or  flat  epithelial  cells. 

The  arteries  of  the  testes  are  branches  of  the  internal  spermatic 
artery,  which  proceed  in  part  from  the  mediastinum  and  in  part  from  the 
tunica  vasculosa  to  the  septula  testis,  and  from  there  break  up  into 
capillary  networks  which  surround  the  seminiferous  tubules.  The  veins 
arising  from  these  networks  follow  the  course  of  the  arteries.  The 
numerous  lyvipJi-vesscls  form  a  plexus  beneath  the  tunica  albuginea, 
which  is  in  cortimunication  with  the  fairly  close  network  of  lymph  capil- 
laries enveloping  the  seminiferous  tubules.  The  nerves  form  networks 
about  the  blood-vessels  ;  whether  single  fibers  branch  off  from  these 
networks,  pierce  the  membrana  propria  of  the  seminiferous  tubules  and 
terminate  in  club-shaped  endings  between  the  epithelial 'cells  is  not  yet 
definitely  established. 

The  Semen. 

The  secretion  of  the  testes,  the  semen  (sperm),  consists  almost  ex- 
clusively of  semen  filaments  (spermatofilia,  spermatozoa),  pin-shaped 
structures  about  60  //  long  in  which  a  head  and  a  tail  are  distinguished 
(Fig.  263).  In  man  the  Jiead  is  from  3  to  5  fi  long,  and  from  2  to  3  ij. 
broad,  flattened,  viewed  from  the  side  pyriform  in  shape,  with  the  taper- 
ing" end  directed  forward,  seen  from  surface  oval,  with  the  anterior  end 
rounded  and  containing  a  clear  division  (Fig.  263,  i).  The  foremost  end 
of  the  head  is  characterized  by  its  density,  which  is  due  to  a  special  struc- 

*  Whence  the  "spermatoblast"  of  authors,  see  Technic  No.  147,  p.  369. 


THE    REPRODUCTIVE    ORGANS.  34 1 

ture,  the  cap,  that  in  man  has  not  yet  been  definitely  demonstrated.  The 
tail  when  very  highly  magnified  exhibits  a  fiber  extending  from  end 
to  end,  the  axial  fiber,  which  is  composed  of  delicate  fibrils.  Three  dif- 
ferent divisions  are  recognized  in  the  tail  :  the  round  connecting  piece 
(middle-piece)  lying  next  to  the  head,  which  is  6  //  long  and  scarce  i  ii 
broad ;  following  this  is  the  main-piece,  from  40  to  60  fx  long,  gradually 
tapering  backwards  ;  the  tip  of  the  tail,  the 
end-piece,  is  about  10  //  long  and  consists  of 
the  projecting  axial  fiber.* 

The  spermatozoa  are  distinguished  by 
their  extraordinary  stability  (probably  due 
to  the  calcareous  substances  which  the\- 
contain). 

The  sinuous  movements  of  the  sper- 
matozoa  are   executed   by  the   tail   alone, 

1  1  1  1     1      r  ■  ^'*^'  ^^3- — ^     ^-    ^-  Human   Spermato- 

which    propels    the    head    before  it ;     they  zoa.    x  360.    i.  view  from  the  sur- 

face.    2.  View  in  profile.     3.  Looped 

seldom   occur  in  the    concentrated    secretion  semen  filament      4-  spermatozoon  of 

an  ox;    a.  head;  0,  connectmg-piece; 

of  the  testis  and  begin   onlv  after  dilution  fi,  "!?'""P'^"-    Tjie  '^"d-piece  and 

t>  -  the   demarcation  of   these   parts  can- 

of  the  semen  normally  effected  by  admix-  ^^-^l  xedJnk  Xo.'ms*!''  ™'^'^^" 

ture   of  the   secretion    of  the    epididymis, 

the  ampullfe,  the  seminal  vesicles,  the  prostate  gland,  and  the  bulboure- 
thral glands  (Cowper).  In  this  mixture  of  fluids  the  motions  may  con- 
tinue for  from  twenty-four  to  forty-eight  hours  after  death  and  for  a  still 
longer  period  in  the  secretions  of  the  female  genitalia.  Water  paralyzes 
the  movement,  which,  however,  ma\'  be  restored  by  the  addition  of  normal 
animal  fluids  of  alkaline  reaction  and  moderate  concentration  ;  normal 
fluids  in  general,  also  a  one  per  cent,  salt  solution,  exert  a  favorable  influ- 
ence on  the  motility  of  the  spermatozoa,  while  acids  and  metallic  salts 
suspend  it.  In  motionless  spermatozoa  the  tail  is  frequently  looped 
(Fig.  263,  3). 

The  Se:\iixal  Passages. 

The   seminal   passages  are  formed  by  the  epididymis,   the   ductus 
deferens,  the  seminal  vesicle,  and  the  ductus  ejaculatorius.f 

From  the  upper  end  of  the  rete  testis  about  fifteen  ductnli  effercntes 


*  The  different  forms  of  semen  filaments  in  animals  cannot  be  considered  here.  The 
spiral  fiber ,  that  is  united  to  the  axial  fiber  by  a  hyaline  membrane,  first  discovered  in  birds  and 
tailed  amphibians,  has  also  been  found  in  mammals,  e.  g.  in  the  rat,  and  appears  to  occur  also 
in  man. 

I  The  tubuli  recti  and  rete  testis  also  belong  t£>  the  seminal  passages,  but  because  of  their 
situation  in  the  interior  of  the  gland  thev  were  described  with  it. 


342 


HISTOLOGY. 


testis  emerge,  which  by  their  progressively  increasing  convolutions  form 
as  many  conical  lobules,  the  lobuli  epididyniidis.  The  aggregate  of  the 
lobules  constitutes  the  so-called  liead  of  the  epididymis.       By  the  union 


•-'■  Tangential  section  of 
a  ductulus  efferens. 


Blood-vessel. 


Epithelium      Ring  muscles 
of  the  ductus  epididymidis. 


Transverse  section  of  a 
ductulus  efferens. 


Connective 
tissue. 


Cubical  cells. 


Cylinder  cells. 


Fig.  264. — From  a  Section  through  the  Head  of  the  Epididymis  oe  _  Man.     X  so.    In  the  middle  are 
transverse  sections  of  the  ductus  epididymidis,  on  the  right  of  the  ductuK'efferentes.     Technic  No.  151. 

of  the  ductuli  efferentes  the  ductus  epididymidis  arises,  which  with  its  com- 
plex convolutions  forms  the  body  and  the  tail  of  the  epididymis  and  then 

continues  as  the  ductus  deferens. 
The  ductidi  effer- 
entes are  clothed  by  an 
epithelium  consisting  of 
totally  dissimilar  varie- 
ties ;  groups  of  simple 
ciliated  cylindric  ele- 
ments alternate  with 
clusters  of  cubical  cells 
partly  without  cilia  ;  con- 
sequently the  latter  have 
the  appearance  of  simple 
alveolar  glands,  that  do 
not  always  produce  evagination  of  the  membrana  propria*  (Fig.  265). 

*  In  a  few  cases  instead  of  the  alveoli  there   are  long  branched  ducts,  that   extend  out 
beyond  the  wall  of  the  ductulus  into  the  surrounding  connective  tissue. 


Smooth  muscle-fibers. 


Connective  tissue. 


Fig.  265: — Transverse  Section  of  a  Ductulus  Efferens  Testis 
OF  an  Adult  Man.  The  right-hand  end  of  the  illustration  is 
schematic.  No  cilia  could  be  seen,  although  those  of  the  epithe- 
lium of  the  epididymis  Vifere  well  preserved.  X  360.  Technic  No. 
151- 


THE    REPRODUCTIVE    ORGANS. 


343 


i^^j. 


Epithelium. 

Membrana 
propria. 

Circular  layer  of 
muscle-fibers. 

Loose  connective 
tissue. 


Fig.  266. — Traxs\i;rse  Section  of  a  Hdjian  Ductus  JEpi- 
DiDYJCDis.     X  80.     Technic  No.  151. 


?:|>??i. >'*''' 


The  cells  contain,  besides  a  widely  var}'ing  quantity  of  pigment  granules, 
granules  which  indicate  a  secretory  function  ;  this  view  is  also  supported 
by  the  circumstance  that  vesicular  processes  resembling  drops  of  secre- 
tion are  often  found  on  the  free  surface  of  the  cells,  instead  of  the  cilia 
(Fig.  265).      A  striated  tunica  _ 

propria    and   a  membrane  of  ^-  ,        '        ->: 

smooth  muscle-fibers,  consist- 
ing of  several  layers  of  circu- 
larly arranged  elements  inter- 
laced with  elastic  fibers,  com- 
plete the  wall  of  the  ductuli 
efiferentes. 

The    ductus    epididyuiidis 
possesses   a   two-row   epithe- 

hum  (Fig.  266), the  elements  of  which  are  spherical  basal  cells  and  long  cyl- 
inder cells  ;  the  latter  contain  secretion  granules  and  on  the  middle  of  their 
free  surface  support  long  hairs,  that  do  ;/<;:'/ vibrate  and  in  fixed  preparations 
are  frequently  glued  together  in  a  conical  process.     In  the  epithelium  tubes 

or  sack-like  ducts,  partly 
closed,  partly  opening  on 
the  free  surface,  are  found. 
A  delicate  membrana  pro- 
pria and  a  thick  layer  oi 
circular  muscle  complete 
the  wall  of  the  ductus  epi- 
didymidis,  the  convolu- 
tions of  which  are  held 
together  by  loose  connec- 
tive tissue  ;  toward  the 
ductus  deferens  the  circu- 
lar muscle  stratum  be- 
comes thicker. 

The  ductus  deferens 
consists  either  of  a  two- 
row  cylinder  epithelium  or 
of  a  stratified  squamous 
epithelium  (resembling  transitional  epithelium,  p.  330)  ;  of  a  connective- 
tissue  tunica  propria,  that  outwardly  is  attached  to  a  dense  plexus  ot 
elastic  fibers  ;  further  of  an  inner  longitudinal,  a  middle  circular,  and  an 
outer  longitudinal  layer  of  smooth  muscle-fibers,  of  which  the  inner  longi- 
tudinal layer  is  especially  well  developed  in  the  initial  portion  of  the  due- 


_  Epithelium. 


.  Tunica  propria. 


-Inner  longitu- 
dinal layer. 


-Ring  layer. 


CIV 


•■^^■• 


■50- 


m 


-% 


-Outer  longitu- 
dinal laver. 


Connective 
tissue. 


='*J^ri»i?'!'"" 


Fig.  267. — Transverse  Section  of  the  Initial  Portion  of  the 
Ductus  Deferens  of  Man.  X  24.  The  transverse  sections  of 
the  longitudinal  muscles  have  the  appearance  of  smaU  circles  and 
dots.    Technic  No.  151. 


344  HISTOLOGY. 

tus  deferens  ;  and  finally,  of  a  connective-tissue  adventitia  intermixed  with 
elastic  fibers  (Fig.  267).  The  latter,  particularly  in  the  division  between 
the  testis  and  the  ejaculatory  duct,  contains  longitudinal  bundles  of  smooth 
muscle-fibers.*  The  terminal  portion  of  the  ductus  deferens  expands  into 
the  ampidla,  the  musculature  of  which  is  more  irregularly  constructed  ; 
between  the  circular  muscles  oblique  and  longitudinal  strands  occur,  while 
the  longitudinal  muscles  break  up  into  isolated  strands,  that  toward  the 
ejaculatory  duct  wholly  disappear.  The  mucous  membrane  of  the  ampulla 
and  of  the  seminal  vesicle  is  laid  in  "  primary  "  folds,  that  in  turn  subdi- 
vide in  secondary  and  tertiary  folds  ;  from  this  develop  diverticula  and 
branched,  tube-shaped  processes  (glands  ?),  that  may  extend  deep  into  the 
muscularisf  and  contain  homogeneous  or  finely  granular  balls  of  secre- 
tion. On  the  primary  folds  the  epithelium  is  a  stratified  (perhaps  only 
many-rowed),  elsewhere  a  simple  cylinder  epithelium,  the  cells  of  which 
contain  pigment  granules  in  widely  varying  quantities. 

The  ductus  ejacidaiorii  on  their  dorso-median  side  are  beset  with  a 
series  of  appendages  that  do  not  project  externally,  but  are  v/holly  en- 
closed in  the  connective-tissue  wall  of  the  duct.  Some  of  these  append- 
ages show  the  same  structure  as  the  seminal  vesicles  and  therefore  might 
be  described  as  accessory  seminal  vesicles  ;  others  are  simply  convolu- 
tions of  alveolo-tubular  glands,  that  may  be  compared  with  the  prostate 
gland.  The  mucous  membrane  of  the  ductus  ejaculatorii  is  like  that  of 
the  seminal  vesicles,  except  that  the  folds  are  not  so  complicated  ;  a 
musculature  is  found  only  on  the  processes,  not  in  the  wall  of  the  duct, 
which  is  formed  of  inner  circular  strands  of  compacter  (the  "  fiber  mem- 
brane") and  outer  looser  connective  tissue  (the  "  adventitia"). J 

The  blood-vessels  of  the  epididymis,  scarce  in  comparison  with  those 
of  the  testis,  lie  on  the  ductuli  efferentes,  in  part  close  beneath  the 
membrana  propria,  which  occasionally  they  evaginate  toward  the  epi- 
thelium. The  veins  of  the  pampiniform  plexus  often  have  thick  walls 
containing  circular  and  longitudinal  muscles. 

In  addition  to  the  networks  around  the  blood-vessels,  the  nerves 
form  a  close  plexus  provided  with  sympathetic  ganglia,  the  plexus  myo- 
spermatiais,  that  lies  partly  in  the  muscularis  of  the  epididymis,  but 
chiefly  in  that  of  the   ductus   deferens  ;  delicate   fibers  arise   from   this 


*  They  really  belong  to  the  tunica  vaginalis  of  the  spermatic  cord  and  are  known  as  the  in- 
ternal cremaster  muscle. 

f  Sections  give  a  very  complicated  picture,  that  can  only  be  correctly  interpreted  by  the 
reconstruction  of  serial  sections. 

\  In  the  outer  strata  of  the  adventitia  isolated  strands  of  smooth  muscle-fibers  occur,  which 
belong  to  the  pelvic  fascia  and  are  in  part  connected  with  the  muscle-fibers  of  the  prostate. 


THE  REPRODUCTIVE  ORGANS. 


345 


plexus,  which  end  for  the  greater  part  on  smooth  muscle-fibers,  for  the 
lesser  part  they  continue  into  the  mucous  membrane. 

Tht  paradic/ymis  (Giraldes),  lying  between  the  elements  of  the  seminal 
cords,  and  the  ditctulits  aberrans  are  atrophic  remains  of  the  embryonal  meso- 
nephros.  Both  consist  of  a  tubule  lined  with  cubical  or  cylindric  ciliated  epi- 
thelium, which  is  enveloped  in  a  vascular  connective  tissue.  The  appendix 
testis  (hydatid  of  Morgagni)  is  a  solid  lobule  composed  of  a  highly  vascular 
connective  tissue,  which  is  covered  with  a  ciliated  cylinder  epithelium  \  it  pos- 
sesses a  short  pedicle,  which  contains  a  little  canal  that  is  lined  with  cylinder 
epithelium.  The  inconstant  appendix  epididymidis  is  a  vesicle  clothed  with 
cubical  epithelial  cells  and  contains  a  clear  fluid.  The  meaning  of  these  ap- 
pendices has  not  yet  been  satisfactorily  explained;  it  is  uncertain  whether 
they  are  remains  of  the  anterior  end  of  the  embryonal  Miillerian  duct,  that  in 
the  female  becomes  the  oviduct,  or  remnants  of  the  primitive  kidney. 


Accessory  Glands  of  the  Male  Sexual  Organs. 

The  prostate  consists  of  gland  substance,  of  smooth  muscle-fibers, 
that  make  up  about  one-fourth  of  the  bulk  of  the  organ,  and  of  con- 
nective tissue,  intermixed  with  rela- 
tively few  elastic  fibers.  The  gland 
substance  is  composed  of  from 
thirty  to  fifty  branched  alveolo- 
tubular  serous  simple  glands,  which 
are  characterized  by  their  loose 
structure.  The  glands  open  by 
two  large  and  a  number  of  smaller 
excretory  ducts  into  the  urethra. 
The  gland-cells  are  low  cylinder 
elements,  which  in  a  simple  layer 
clothe  the  tubules.  In  the  larger 
excretory  ducts  the  epithelium  is 
of  the  transitional  variety  (p.  330), 
like  that  in  the  prostatic  portion 
of  the  urethra.  In  elderly  persons 
the  so-called  prostatic  crystals, 
round,  stratified  masses  of  secre- 
tion up  to  0.7  mm.  in  size,  occur 
in  the  end-pieces.  The  smooth 
muscle-fibers  found  in  large  quan- 
tities everywhere  between  the 
gland  lobules,  are  augmented  to- 
ward the  urethra  and  form  a  robust  circular  layer  (the  internal  vesical 
sphincter  muscle)  ;    numerous  smooth  muscle-fibers  are  also  found  on 


.  26S. — From  a  Section  of  the  Prostate  of  a 
Condemned  Man  22  Years  Old.  X  53.  Technic 
No.  152. 


346  HISTOLOGY. 

the  external  surface  of  the  prostate  gland,  where  they  are  contiguous  to 
the  bundles  of  striated  muscle-fibers  of  the  musculus  sphincter  urethrae 
membranacese.*  The  prostate  and  the  colHculus  seminalis  are  provided 
with  many  blood-vessels.  The  numerous  nerves  form  wide-meshed  net- 
works containing  nerve-cells  ;  of  the  nonmedullated  fibers  arising  from 
these  networks  some  approach  the  smooth  muscle-fibers,  some  end  in  free 
ramifications,  some  (in  dogs  and  cats)  terminate  in  special  end  apparatus 
(p.  224),  that  are  found  in  the  capsule  and  in  the  interior  of  the  organ. 

The  bulboiiretliral  glands  (glandule  bulbourethrales,  Cowper)  are 
compound  alveolo-tubular  glands  ;  the  irregularly  widened  excretory 
duct  sends  off  similarly  constructed  branches,  that  are  annexed  either 
directly  or  indirectly,  by  means  of  intercalated  tubules,  to  the  end- 
pieces.  The  latter  have  the  form  of  tubules  and  of  spherical  vesicles 
or  of  transition  forms  of  both.  Occasionally  reticular  connection  of 
the  end-pieces  occurs.  The  branches  of  the  excretory  duct  are  lined 
with  a  low,  simple  epithelium  and  encircled  by  thin  rings  of  smooth 
musculature.  The  terminal  pieces  possess  gland-cells  resembling  mu- 
cous cells  and  intercellular  secretory  capillaries.  Between  the  gland 
lobules  lie  many  smooth  and  striated  muscle-fibers. 

The    Penis. 

The  penis  consists  of  three  cylindrical  erectile  bodies  :  the  two 
corpora  cavernosa  penis  and  the  corpus  cavernosum  urethrae,  which 
are  enveloped  in  fascia  and  skin. 

Each  corpus  cavernosinn  penis  consists  of  a  tunica  albuginea  and  of  an 
erectile  tissue.  The  tunica  albuginea  is  a  stout  connective-tissue  mem- 
brane, intermingled  with  many  delicate  elastic  fibers,  possessing  an  aver- 
aee  thickness  of  one  mm.,  in  which  an  outer  longitudinal  and  an  inner  cir- 
cular  layer  can  be  distinguished.  The  erectile  tissue  is  constructed  of 
lamelke  and  trabeculae  of  connective  tissue  containing  bundles  of  smooth 
muscle-fibers,  that  by  means  of  numerous  anastomoses  form  a  network. 
The  spaces  of  the  net  are  clothed  with  a  simple  stratum  of  flat  epithelial 
cells  and  are  filled  with  venous  blood.  The  thick-walled  arteries  in  part 
pass  into  capillaries  that  form  a  network  situated  beneath  the  tunica 
albuginea,  the  superficial  {fine)  cortical  plexus;  this  is  connected 
with  a  many-layered  net  of  wider  venous  vessels,  the  deep  (coarse)  cor- 
tical plexus,  that  lies  in  the  superficial  strata  of  the  erectile  tissue  and 
passes  into  the  venous  spaces  of  the  same.  'Some  of  the  arteries 
open   directly  into    the    deep  cortical    plexus.      The    so-called    helicine 

*  Both  sphincters  are  now  included  in  the  designation  musculus  prostaticus. 


THE  REPRODUCTIVE  ORGANS. 


347 


arteries  are  small  branches  lying  within  slender  strands  of  connective 
tissue,  which  in  the  collapsed  organ  are  bent  in  the  form  of  a  loop  and  in 
an  imperfect  injection  appear  to  terminate  in  blind  ends.  The  veins 
(venfe  emissarije)  which  return  the  blood  from  the  corpora  cavernosa 
penis  partly  arise  from  the  deep  cortical  plexus,  partly  from  the  depths 
of  the  erectile  tissue.  They  penetrate  the  tunica  albuginea  and  empty 
into  the  dorsal  vein  of  the  penis. 

The  corpus  cavenwswn  iiretlircB  consists  of  two  different  divisions  ; 
the  central   portion  is   formed  by  a  reticulum   of  the  conspicuously  de- 


Epithelium 


Mucous  membrane  of  the  urethra. 
Tunica  propria.        Urethral  glands. 


\ 

Tunica 
albuginea. 


Arteries. 


Connective  tissue 
trabeculie. 


Bundles  of  smooth 
muscle. 


Cavernous  spaces. 
Fig.  269. — Transverse  Section  of  the  P.ars  Cavernosa  Urethr.e  of  Man.     X   28.    TechniclNo.  152. 


veloped  veins  of  the  submucosa  of  the  urethral  mucous  membrane  (p. 
333)  ;  the  peripheral  portion  in  structure  resembles  the  corpus  cavernosum 
penis,  excepting  that  there  is  no  direct  communication  of  the  arteries 
with  the  venous  spaces.  The  tunica  albuginea  is  composed  simply  of  a 
layer  of  circularly  arranged  bundles  of  connective  tissue.  The  glans  penis 
consists  of  greatly  convoluted  veins,  that  are  held  together  by  a  con- 
spicuously well-developed  connective  tissue,  containing  many  elastic 
fibers  and  supporting  the  arterioles  and  the  capillaries.  (For  the  skin 
of  the  glans,  see  p.  589.) 


348  HISTOLOGY. 

In  the  tunica  albuginea  of  the  corpora  cavernosa,  in  the  glans,  and 
also  in  the  prepuce  pecuHar  terminal  organs  of  nerves  are  found  (p.  224). 

THE  FEMALE  REPRODUCTIVE  ORGANS. 

The  Ovaries. 

The  ovaries  consist  of  connective  tissue  and  of  gland  substance. 
The  compact  connective  tissue,  the  ovarian  stroma,  is  arranged  in  several 
strata;  outermost  lies  (i)  the  tunica  albuginea  (Fig.  270),  a  thick  struc- 
ture in  man,  composed  of  two  or  more  intersecting  lamellae  of  connective 
tissue,  which  pass  by  imperceptible  gradations  into  (2)  the  cortex ;  the 
latter  encloses  the  gland  substance  and  is  continuous  with  (3)  the  medulla, 


Fig.  270. — Transverse  Section  of  the  Ovary  of  a  Child  Eight  Years  Old.  X  lo.  i.  Germinal  epithe- 
lium; 2,  tunica  albuginea;  3,  outermost  zone  of  the  cortex  containing  numerous  minute  follicles;  4,  larger 
follicle;  5,  inner  division  of  cortex;  6,  medulla  with  numerous  tortuous  arteries;  7,  follicle  cut  at  the  peri- 
phery; 8,  large  follicle,  the  cumulus  oophorus  not  within  the  plane  of  the  section;  9,  hilus,  containing  wide 
veins.     Technic  No.  135. 

which  is  rich  in  elastic  fibers  and  contains  numerous  convoluted  vessels 
accompanied  by  strands  of  smooth  muscle-fibers.  The  gland  substance 
is  formed  by  a  profusion  of  spherical  epithelial  sacs,  the  egg-follicles,  each 
of  which  contains  an  egg-cell.  In  the  human  ovary  there  are  about 
36,000  follicles.  The  majority  of  the  follicles  are  microscopically  small 
(40  //)  and  in  the  outer  strata  of  the  cortex  form  an  arched  zone  embrac- 
ing the  entire  organ  except  at  the  hilus,  the  place  where  the  vessels  enter 
(Fig.  270).  The  larger  follicles  occupy  somewhat  deeper  portions  of 
the  cortex.  The  largest,  those  follicles  readily  perceptible  by  the  unaided 
eye,  when  fully  developed  extend  from  the  medulla  to  the  tunica  albu- 
ginea. The  surface  of  the  ovary  is  covered  with  a  simple  layer  of  very 
small,  short  cylindrical  or  flat  cells,  the  germinal  epitheliinn. 


THE    REPRODUCTIVE    ORGANS. 


349 


Germinal 
Egg-ball.      epithelium. 


Only  the  initial  stage  in  the  development  of  the  egg-cells  takes  place 
during  embryonal  life ;  their  subsequent  development,  from  the  primordial 
to  the  fully  ripened  cell,  may  be  observed  in  all  its  phases  in  every 
functionally  active  ovary.  During  the  fetal  period  many  cells  of  the 
germinal  epithelium  divide  into  two  cells  Ij'ing  one  above  the  other,  of 
which  the  lower  enlarges 
and  becomes  the  primordial 
egg-cell  with  its  large  nu- 
cleus and  nucleolus,  while 
the  upper  cell  and  also  its 
neighbor-cells  become  flat- 
tened and  place  themselves 
shell-like  around  the  ovum. 
Such  conditions  are  still 
found  after  birth  (Fig.  271). 

The  egg-cell,  which  under  circumstances  may  divide  again,  sur- 
rounded by  its  indifferent  neighbor-cells,  now  moves  down  into  the  ovarian 
stroma,  while  above  in  the  germinal  epithelium  new  primordial  eggs  arise 


Germinal  spot,     j^' 
S  \    Germinal  vesicle.  4^^ 
Vitellus 


Follicular 
epithelium. 


Fig.  2-1. — From  a  Vertical  Section  of  the  Ovary  of  an  In- 
fant Four  Weeks  Old.  X  240.  The  primordial  egg-cell  has 
a  large  nucleus  with  a  nucleolus.  The  egg-ball  contains  three 
egg-cells,  surrounded  by  cylinder  cells.     Technic  No.  153. 


FoUicular  epithehum.  Germinal  vesicle.  Germinal  spot.        Vitellus.        Oolemma. 

Fig.  272. — From  a  Section  of  the  Cortex  of  a  Rabbit's  Ovary.     X  240     Technic  No.  153. 


in  the  same  way,  that  likewise  move  into  the  depths.  Thus  originate  en- 
tire complexes  of  egg-cells  and  indifferent  cells  of  the  germinal  epithelium, 
complexes  which  are  named  egg-balls  (egg-pouches,  egg-nests).  Each 
egg-cell  subsequently  becomes  separated  from  its  neighbors  by  the  rapid 
multiplication  of  the  indifferent  epithelial  cells,  as  well  as  by  proliferation 
of  the  connective  tissue,  and  is  then  an  isolated  spherical  body,  the 
primitive  follicle,  that  consists  of  the  &^a  and  the  epithelial  cells  enclos- 
ing it,  the  so-called  follicular  epithelium,  and  of  a  connective-tissue  sheath. 


350 


HISTOLOGY. 


So  far  the  processes  are  chiefly  fetal.*  The  cells  of  the  follicular  epithe- 
lium now  grow  taller  (Fig.  272,  below  left),  then  become  stratified,  the 
egg  grows  larger,  takes  up  an  eccentric  position  within  the  follicle,  and 
obtains  a  delicate,  radially  striated  border  stratum  that  gradually  increases 
in  thickness,  the  zona  pelhicida  (oolemma).  With  the  enlargement  of  the 
egg  a  differentiation  of  its  protoplasm  is  also  accomplished ;  the  greater 
portion  of  it  is  transformed  into  a  crummy  mass,  the  deutoplasm ;  only  a 
zone  around  the  eccentrically  situated  nucleus  and  a  thin  stratum  cover- 
ing the  surface  of  the  egg  are  distinguished  by  a  more  abundant  quantity 


, 

^.j.    \  Tunica  externa. 

II 

"^  .2    L   Tunica  interna. 

4>y 

'    ' '  /  „• 

,^;-X-V 

m-i 

I';/.;- 

Stratum  granulosum. 
(Follicular  epithe- 
lium.) 

I'l^'xi: 

.    ;,  "% 

kf.':V 

'  'm"i 

Cumulus  oophorus. 

—  ^^^ 

v;- 


Egg-cell  with  zona  pellu- ' 
cida,  germinal  vesicle, 
and  germinal  spot. 


^^v\-:'*A 


y 


Fig.  273. — Section  of  a  Large  Vesicular  Follicle  of  a  Child  Eight  Years  Old.     X  90.    The  clear 
space  within  the  follicle  contains  the  liquor  folliculi.     Technic  No.  153- 

of  the  original  protoplasm,  the  egg  protoplasm.  The  deutoplasm  and  the 
egg  protoplasm  are  together  named  vitellus,^  the  nucleus  is  called  the 
germinal  vesicle  (vesicula  germinativa),  which  contains  the  germinal  spot 
(macula  germinativa).  Ameboid  movements  have  been  observed  in  the 
latter.     The  full-grown  human  egg  has  a  diameter  of  about  0.3  mm. 

The  follicle  now  develops  further  ;   during  continual  multiplication 


*  In  a  few  cases  egg-balls  and  egg-cells  with  several  germinal  vesicles  are  found  in  sexually 
mature  individuals,  which  represent  elements  in  which  the  division  of  the  cell-body  has  not  yet 
taken  place  or  perhaps  they  are  an  effect  of  pressure,  that  is  two  separate  egg-cells  were  so 
pressed  together  that  their  dividing  line  disappeared. 

f  The  nucleus  of  the  vitellus,  long  known  in  animals,  has  recently  been  found  in  the 
human  egg;   it  corresponds  to  the  centrosome  or  to  the  archoplasm  (p.  65). 


THE  REPRODUCTIVE  ORGANS. 


351 


of  the  cells  of  the  follicular  epithelium  a  cleft  appears  in  their  midst  that 
becomes  filled  with  an  aqueous  fluid,  the  liquor  follicnli.  This  liquor  is 
partly  a  transudate  from  the  blood-vessels  surrounding  the  follicle,  is 
partly  derived  from  the  liquefaction  of  some  of  the  cells  of  the  follicular 
epithelium  ;  it  undergoes  progressive  increase  in  quantity  and  conse- 
quently the  follicle  soon  expands  to  a  vesicle  filled  with  fluid,  the  vesicular 
follicle  (Graaf),  having  a  diameter  of  from  0.5  to  12  mm.  Around  the 
larger  follicles  the  connective  tissue  of  the  stroma  is  arranged  in  circular 
strands  forming  a  sheath  called  the  theca  folliculi,  in  which  an  outer 
fibrous  layer,  the  tunica  externa,  and  an  inner  vascular  layer  rich  in  cells, 
the  tunica  interna,  can  be  distinguished  (Fig.  272).  Thus  the  follicle 
consists  of  a  connective  tissue  sheath,  the  theca  folliculi,  and  of  the  strati- 
fied follicular  epithelium  (Fig.  273),  which  in  teasing  fresh  follicles  be- 


-^/- 


Zona  pellucida. 
ViteUus. 

Cells  of  the  cu- 
mulus oophorus. 


V'^^s&SilS 


Ct'4 

J    "-" 

■J-- 

■j^ 

Zona  peUucida. 


Vitellus. 


Germinal 
vesicle. 
Germinal  spot. 


Corona  radiata 
(cells  of  the 
cumulus). 


Fig.  274. — An  Ovum  from  a  Vesicular  Follicle  of  a  Cow.    A  magnified  50,  B  magnified  240  times.    The 
radial  striation  of  the  zona  peUucida  cannot  be  seen.     Technic  No.  154. 

comes  detached  in  large  shreds,  and  has  long  been  known  as  the  stratum 
{inenibrana^  granulosuni ;  *  at  one  point  it  presents  a  thickening,  the 
cumulus  oophorus,  which  enclo.ses  the  &^'g.  The  cells  of  the  cumulus 
which  lie  next  to  the  zona  peUucida  are  radially  placed  to  the  &^^  and 
form  the  corona  radiata  (Fig.  274).  The  greater  part  of  the  interior 
space  of  the  follicle  is  occupied  by  the  liquor  folliculi. 

When  the  vesicular  follicle  has  attained  its  full  development  it 
bursts  at  the  side  directed  toward  the  surface  of  the  ovary,  where  its 
site  is   previously  indicated    by  the  attenuated    and    arched    overlying 


*  Between  the  tunica  interna  and  the  follicular  epithelium  a  delicate  membrana  propria  is 
found  in  man,  that  in  animals  is  often  replaced  by  a  thin  ring  fiber-layer. 


352 


HISTOLOGY. 


tissue  ;  the  egg-cell  escapes  into  the  pelvic  cavity,  the  empty  follicle 
undergoes  regressive  change  and  is  converted  into  the  yellow  body,  the 
corpus  luteiim.  When  the  discharged  &^g  is  not  fertilized  the  yellow  body 
disappears  after  the  lapse  of  a  few  weeks  ;  if  on  the  other  hand  pregnancy 
occurs,  the  ruptured  follicle  develops  into  a  large  body,  that  possesses  a 
diameter  up  to  three  centimeters  and  endures  for  years.  At  first  it  con- 
sists of  a  fibrous  membrane,  the  former  tunica  externa  of  the  theca,  and 
of  a  yellow  mass,  that  is  formed  of  large,  fatty  cells,  the  lutein  cells, — the 
multiplied  and  enlarged  elements  of  the  follicular  epithelium— -between 
which  delicate  connective-tissue  septa  occur,  derivatives  of  the  connec- 
tive-tissue tunica  interna  of  the  theca  foUiculi  (Fig.  275). 


Connective-tissue  septa 

A 


Fibrous  membrane. 


Oil-droplets. 


Lutein  cells. 


Fig.  275. — A.  Portion  of  a  Corpus  Luteum  or  a  Rabbit.    B.  Portion  of  a  Corpus  Luteum  of  a  Cat 
X  260.     In  B  the  lutein  cells  have  become  fatty  and  contain  large  and  srnall  oil  droplets.     Technic  No.  153. 


In  the  center  of  the  corpus  luteum  is  a  gelatinous  connective  tissue 
and  occasionally  a  cavity  filled  with  blood.  The  blood  is  derived  from 
the  torn  vessels  of  the  tunica  interna.  Later  the  center  becomes  decol- 
orized and  the  blood  is  replaced  by  a  crummy  mass,  occasionally  con- 
taining hematoidin  crystals  (see  page  139). 

Not  all  the  primitive  follicles  attain  complete  development.  Many 
undergo  regressive  change.  Retrograde  metamorphosis  of  larger  follicles 
also  occurs.* 

*  The  process  is  effected  in  this  wise  :  the  tunica  interna  of  the  theca  folliculi  increases 
greatly  in  thickness,  during  which  the  egg  dies;  then  cells,  partly  elements  of  the  stratum 
granulosum,  partly  leucocytes,  wander  into  the  egg  and  liquefy  and  absorb  its  substance.  After 
the  migratory  cells  have  accomplished  the  liquefaction  and  resorption  of  the  material  of  the 
vitellus  they  perish.  Such  degenerating  follicles  are  called  at7'etic  follicles ;  they  are  easily 
recognized  by  the  wrinkled  oolemma,  the  part  of  the  egg  which  persists  the  longest  (Fig.  272, 
' '  A  perishing  egg  "  ) . 


THE  REPRODUCTIVE  ORGANS.  353 

The  arteries  of  the  ovary,  branches  of  the  ovarian  and  the  uterine 
arteries,  enter  at  the  hilus,  divide  in  the  medulla,  and  are  characterized 
by  their  tortuous  course  (Fig.  270).  From  the  medulla  they  pass  to 
the  cortex,  where  they  chiefly  supply  the  capillary  networks  situated 
in  the  tunica  interna  of  the  follicles.  The  vems  form  a  dense  plexus 
at  the  hilus  of  the  ovary.  The  numerous  Ijinph-vesse/s  can  be  traced 
to  the  tunica  interna  of  the  follicles.  Medullated  and  nonmedul- 
lated  nerves  in  large  number  enter  the  medulla  through  the  hilus,  in 
company  with  the  blood-vessels,  to  the  walls  of  which  the  majority 
of  them  are  distributed.  A  {^w  of  the  nerves  proceed  to  the  cortex  ; 
these  form  there  a  dense  plexus  of  delicate,  mostly  nonmedullated 
fibers,  which  envelops  the  follicles  and  sends  minute  branches  to  the  walls 
of  the  blood-vessels  ;  whether  nerve-fibers  penetrate  within  the  epithe- 
lium of  the  larger  follicles  is  not  yet  definitely  established. 

The  epooplioron  and  the  parodphoro7i  are  remains  of  embryonal 
structures.  The  former  lies  within  the  lateral  division  of  the  mesosal 
pinx,  at  the  hilus  ovarii  (in  the  cat,  mouse,  etc.,  in  rare  cases  also  in  man 
within  the  hilus),  and  consists  of  a  group  of  convoluted,  blind-ending 
tubules,  the  walls  of  which  consist  of  cylinder  epithelium,  occasionally 
ciliated,  and  of  circularly  arranged  connective-tissue  fibers.  The  epoopho- 
ron  is  a  remains  of  the  sexual  segment  of  the  primitive  kidney.  The 
paroophoron  lies  in  the  median  division  of  the  mesosalpinx  *  and  con- 
sists of  branched  tubules  lined  with  cylinder  epithelium  ;  it  is  also  a 
remains  of  the  mesonephros. 

The  Oviduct.  ' 
The  wall  of  the  oviduct  {tuba  uterina,  Fallopia)  consists  of  three 
membranes  :  an  inner  mucous  membrane,  a  middle  muscular  membrane 
and  an  outer  serous  envelop.  The  mucous  inembraue  is  thrown  into 
numerous  longitudinal  folds,  that  correspond  in  amplitude  to  the  size  of 
the  tube,  and  are  highest  in  the  ampulla,  where  they  are  united  to  one 
another  by  minute  oblique  secondary  plications.  The  thick  mucous 
membrane  consists  of  {a)  a  simple  layer  of  ciliated  cylinder  epithelium, 
— the  ciliary  wave  is  directed  toward  the  uterus,  and  of  {p)  a  tunica 
propria  rich  in  connective-tissue  cells,  that  lies  close  against  the  muscle 
membrane,  t 

*  According  to  recent  investigations  the  paroophoron  is  said  to  correspond  to  structures  be- 
neath and  external  to  the  attachment  of  the  raesovarium,  that  are  to  be  sought  along  the  free 
edge  of  the  broad  ligament. 

f  Longitudinal  strands  of  smooth  muscle-fibers  lying  close  beneath  the  tunica  propria  in 
a  few  places,  by  some  authors  are  described  as  muscularis  mucosae. 
23 


354  HISTOLOGY. 

The  muscular  inembraiie  consists  of  an  inner  thick  circular  and  an 
outer,  in  places  thin,  longitudinal  layer  of  smooth  muscle-fibers.  The 
serous  tunic  is  formed  by  the  peritoneum  and  by  a  conspicuous  layer 
of  loosely  united  connective-tissue  bundles.  Elastic  fibers  occur  in  the 
muscularis  and  in  the  serosa,  but  in  children  and  in  old  women  are  con- 
fined chiefly  to  the  serosa.  The  highly  developed  blood-vessels  between 
the  circular  and  the  longitudinal  layer  of  the  muscularis  send  or  receive 


^ 


% 


''It  Pi' 


Serosa. 


Longitudinal  muscles. 

\ 
Blood-vessels. 


Circular  muscles. 


Mucosa. 

Fig.  276. — Transverse  Section  of  the  Oviduct  of  an  Adult  Woman  (near  the  Ampulla).     X  so- 

Tedinic  No.  156. 

branches  from  the  mucous  membrane,  which  is  provided  with  a  narrow- 
meshed  capillary  plexus.  The  larger  veins  run  along  the  longitudinal 
folds  of  the  mucosa.  The  knowledge  of  the  exact  behavior  of  the 
lymph-vessels  is  still  wanting.  The  nerves  (in  the  pig)  form  a  rich  plexus 
in  the  mucosa,  from  which  branches  ascend  to  the  epithelium.  A  pene- 
tration in  the  epithelium  has  not  been  observed. 

The  Uterus.* 
The  wall   of.  the    uterus,   like   that   of  the    oviduct,    consists    of   a 
mucosa,  a  muscularis,  and  a  serosa  (Fig.  277). 

*This  chapter  has  been  revised  and  considerably  enlarged  by  the  editor. 


THE    REPRODUCTIVE    ORGANS. 


355 


The  serosa  exhibits  no  special  characteristics. 

The  iiuiscitlaris  consists  of  smooth  muscle-fibers,  united  into  bundles 
which  interlace  in  all  directions,  so  that  a  sharp  demarcation  of  single 
layers  is  not  possible  ;  still  in  general  three  strata,  more  or  less  well- 
defined,  can  be  distinguished:  (i)  an  inner,  the  stratum  siibuiiicosum, 
chiefly  composed  of  bundles  disposed  in  a  longitudinal  direction;  (2)  a 
middle,  the  most  robust,  consisting  of  bundles  having  in  general  a  cir- 
cular disposition  and  containing  wide  veins,  hence  the  name  stratum  vas- 
cidare ;  (3)  an  outer  layer,  the  stratiim  supravasciilare,  formed  of  bundles 
extending  partly  in  a  circular,  partly  in  a  longitudinal  direction,  the 
latter  lying  close   beneath    the    serosa.      The    longitudinal    bundles    of 


Mucosa. 


^.^. 


Muscularis.  (  '' 


Serosa. 


-sssajD 


Fig.  277. — From  a  Transverse  Section  of  the  Middle  of  the  Uterus  of  a  Girl  Fifteen  Years  Old. 
X  10.  a,  Epithelium;  6,  tunica  propria;  c,  glands;  i,  inner  muscular  layer  (stratum  submucosum);  2,  middle 
muscular  layer  (stratum  vasculare);  3,  outer  muscular  layer  (stratum  supra  vasculare).     Technic  No.  156. 


this  stratum  pass  over  into  the  musculature  of  the  oviduct  and  into  the 
surrounding  subserous  connective  tissue  of  the  folds  of  the  peritoneum. 
The  stratification  of  the  muscular  tissue  is  more  pronounced  in  the 
cervix,  where  an  inner  and  an  outer  longitudinal  may  be  distinguished 
from  a  middle  circular  layer.  The  volume  of  the  muscularis  is  subject 
to  great  variation,  dependent  on  the  functional  state  of  the  uterus. 

The  muscle-fibers  differ  somewhat  from  the  elements  of  smooth 
muscle-tissue  found  in  other  organs.  They  are  elongated  cells,  usually 
spindle-shaped,  or  are  blunted  and  frayed  at  the  ends.  Frequently 
they  are  forked  at  their  extremities.  Their  length  varies  greatly,  in  the 
virgin  uterus  from  40  to  60  fi ;   during  pregnancy  they  increase  exces- 


356 


HISTOLOGY. 


sively  and  at  the  end  of  the  same  attain  a  size  of  from  300  to  600  11. 
The  nucleus  (not  infrequently  two  or  more  are  present  in  one  cell)  is 
usually  oval  and  lies  embedded  in  a  granular  substance. 

The  vmcosa  is  sharply  defined  from  the  muscularis.  It  is  the  coat 
which  in  the  different  functional  states  of  the  uterus  undergoes  the  pro- 
foundest  and  physiologically  the  most  important  changes.  Therefore  a 
description  of  the  histologic  structure  of  the  mucosa  of  the  uterus  can 
only  answer  to  the  corresponding  functional  condition  of  the  organ,  and 
in  consideration  hereof  will  be  presented  in  separate  sections. 


*^^-y Epithelium. 


--  Gland  tubule. 


Mucosa. 


yjii 


F^G.  278. — Mucous  MEMBEAisrE  OF  THE  RESTING  Uterus  OF  A  YouNG  WoiLAN.     X  35-     {Ajler  Bohm  and  von 

Davidofj.) 


It  is  desirable  to  consider  : — 

1.  The  mucosa  of  the  virgin  resting  organ. 

2.  The  mucosa  of  the  menstruating  uterus. 

3.  The  mucosa  of  the  gravid  uterus. 

The  mucosa  of  the  virgin  resting  uterus  (Fig.  278),  after  the  advent 
of  puberty,  has  a  thickness  of  from  i  to  2  mm.  and  bears  on  its  surface 
a  layer  of  simple  ciliated  columnar  epithelium,  30//  in  height  in  the  middle 
regions  ;  the  ciliary  wave  is  directed  toward  the  cervix.  The  tunica 
propria  is  formed  of  a  fine  fibrous  tissue  closely  resembling  embryonal 


THE  REPRODUCTIVE  ORGANS. 


357 


connective  tissue  ;  it  consists  of  elongated  cells  furnished  with  oval  nuclei, 
which  send  out  in  all  directions  branched  processes  that  unite  with  those 
of  neio-hborins  cells  and  form  a  cellular  network,  the  meshes  of  which 
are  occupied  by  lymph  and  by  numerous  leucocytes. 

The  tunica  propria  supports  many  simple  or  forked  gland  tubules,  of 
w^hich  the  upper  part  pursues  a  more  or  less  straight  course,  while  the 


Superficial  epithelium. 


Excretory  duct. 


V'v"-vV'"^vJ -j.f:*  *i.',i*''L '^'"^^/^^  ,  ..   -  .  .-. 


'^mM^- 


M 


Excretory  duct. 


Gland  tubule. 


Blood-vessel. 


Blood-vessel. 


Muscularis. 


Fig.  279.— Mucous  Membrane  of  a  Virgin  Uterus  During  the  First  Day  of  Menstruation,  ds.  Disin- 
tegrating surface;  pd,  pit-like  depression  of  the  mucous  membrane;  gl,  gland  lumen  very  much  enlarged. 
X  30. — (Schaper.) 


lower  part  takes  a  serpentine  course  (Fig.  277).  The  glands  extend 
close  to  the  muscularis  and  here  not  infrequently  they  are  bent  at  right 
angles,  so  that  the  fundus  runs  parallel  to  the  muscular  coat.  The 
glands  of  the  uterus  are  to  be  regarded  as  invaginations  of  the  super- 
ficial epithelium  and  likewise  consist  of  a  simple  layer  of  ciliated  epithe- 


358  HISTOLOGY. 

lium,  resting  upon  a  delicate  basement  membrane  composed  of  anasto- 
mosing connective-tissue  cells. 

The  blood-vessels  run  in  a  winding  manner  from  the  muscularis  to 
the  surface  of  the  mucosa  and  the  arteries  in  particular  are  character- 
ized by  their  extremely  convoluted,  corkscrew-like  course.  At  the  sur- 
face they  break  up  into  capillaries  and  form  a  close  network.  A  similar 
network  surrounds  the  gland  tubules.  The  veins  proceeding  from  the 
capillaries  form  a  plexus  in  the  deeper  strata  of  the  mucosa,  that  is  espe- 
cially well  developed  in  the  cervix  and  particularly  around  the  external 
orifice. 

In  the  cervix  the  mucous  membrane  is  thicker  and  in  its  upper  two- 
thirds  is  clothed  with  a  single  layer  of  tall  ciliated  cells  (60  fi  high  in  the 
middle  portion),*  while  toward  the  external  orifice  papillae  covered  with  a 
stratified  squamous  epithelium  appear.  In  addition  to  a  few  scattered 
tubular  glands,  mucous  follicles,  the  so-called  mucous  crypts,  occur  ;  they 
are  one  mm.  wide,  possess  many  evaginations,  'and  by  retention  of  their 
secretion  are  converted  into  cysts,  the  ovida  Nabothi. 

During  the  period  of  menstruation  a  number  of  progressive  and 
regressive  changes  take  place  in  the  mucosa  of  the  uterus,  which  may 
be  grouped  in  three  phases  : — 

[a)  Thickening  of  the  mucosa,  accompanied  by  changes  in  its 
histologic  structure. 

{b)  Menstruation  proper. 

{c)  Regeneration. 

The  initial  phase  is  characterized  by  a  considerable  increase  in  the 
thickness  of  the  mucosa  (up  to  6  mm.),  in  consequence  of  which  the 
surface  becomes  irregular  and  the  orifices  of  the  glands  open  in  deep 
depressions.  The  thickening  of  the  mucosa  depends  in  a  measure  on  an 
actual  increase  of  the  tissue  produced  by  proliferation  of  the  connective- 
tissue  cells  and  the  leucocytes  and  by  growth  of  the  gland  tubules,  which 
in  the  process  take  up  an  irregular  course  and  become  essentially  wider. 
Simultaneously  the  blood-vessels,  especially  the  veins  and  capillaries, 
undergo  enormous  distention,  whereby  the  blood-supply  of  the  organ  is 
extraordinarily  augmented.  In  this  condition  the  mucosa  is  designated 
decidua  menstrualis . 

These  changes  are  followed  by  a  partial  disintegration  of  the  super- 
ficial strata  of  the  mucosa,  accompanied  by  an  infiltration  of  blood  into 
the  subepithelial  tissues.  The  molecular  disintegration  (associated  with 
fatty  degeneration)  of  the  surface  advances  rapidly,  the  greatly  dilated 

*  Transformation  of  these  cells  into  goblet-cells  occurs. 


THE  REPRODUCTIVE  ORGANS, 


359 


superficial  blood-vessels  become  exposed,  rupture,  and  cause  hemor- 
rhages within  the  uterine  cavity,  which  flow  into  the  vagina  and  give  rise 
to  the  external  phenomena  of  inenstriiation.  After  this  discharge  of 
blood  the  mucosa  is  rapidly  reduced  in  thickness.  The  surface  is  now 
entirely  devoid  of  epithelium  and  consists  of  connective  tissue  and  ex- 
posed blood-vessels.  This  condition  is  immediately  succeeded  by  the 
stage  of  regeneration.  The  hyperemia  rapidly  disappears,  the  extrava- 
sated  blood  is  partly  resorbed,  partly  cast  off,  a  cellular  network  grows 
upward  and  restores  the  lost  tunica  propria,  while  from  the  gland-cells 
the  epithelial  covering  of  the  mucosa  is  regenerated.  New  subepithelial 
capillaries  are  formed. 


Compact  layer. 


Cavernous  layer.  \  ■,  '-->■''    \ 

■y'    .<^ 


—    Excretory  duct. 


Spiral  artery. 


Gland  tubules. 


~':'~ .      Muscularis. 


Fig.  280. — Vertical  Section  through  the  Mucous  Membrane  of  a  Human  Uterus  One  Month  Preg- 
nant; it  shows  the  outUnes  of  the  glands  and  the  division  of  the  mucosa  into  an  upper  compact  and  a  lower 
cavernous  layer. — {Ajter  Minol.) 


The  histology  of  the  mucosa  of  the  uterus  during  pregnancy  {decidxxdL 
graviditatis)  (Fig.  280  and  Fig.  281)  is,  on  the  whole,  Hke  that  of  the 
decidua  menstrualis,  with  the  alterations  more  pronounced.  However,  it 
undergoes  considerable  modification  because  of  its  intimate  relations  with 
the  developing  ovum  in  the  uterus.  These  relations  vary  and  thus  in 
the  course  of  development  three  essentially  different  parts  of  the  mucosa 
may  be  distinguished  : — 

(a)  The  decidua  serotiiia  (decidua  basalis),  the  area  of  the  mucosa  to 
which  the  ovum  is  attached  (placenta  uterina). 


36o 


HISTOLOGY. 


(Jy)  The  decidiia  vera,  which  comprises  all  the  remaining  portion  of 
the  mucosa  attached  to  the  wall  of  the  uterus. 

{c)  The  decidtta  rcflexa  (decidua  capsularis),  the  portion  of  the 
mucosa  which  projects  into  the  cavity  of  the  uterus  and  encapsules  the 
ovum. 

The  decidua  serotina  and  the  decidua  vera  undergo  progressive  de- 
velopment during  the  entire  course  of  pregnancy  and  persist  until  its 
close  ;  the  decidua  reflexa  becomes  gradually  attenuated  and  disappears 
in  the  course  of  the  fifth  month. 


Chorion. 


Compact  layer.    < 


Sa'Si  "Zfn^ ^  ego  .  '<J^_  *   -»      ^ 


^ — Gland. 


Cavernous  layer,    i    -f. 


Muscularis. 


•  Vein. 


Fig.  281. — Vertical  Section  through  the  Wall  of  a  Uterus  about  Seven  Months  Pregnant,  with  the 
Fetal  Membranes  in  Situ.  Between  amnion  and  chorion  are  threads  of  the  intermediate  gelatinous  con- 
nective tissue.     X  30. — (Schaper.) 


A  section  of  the  greatly  thickened  mucosa  (decidua  vera  and 
decidua  serotina)  shows  the  same  histologic  details  that  have  been  de- 
scribed in  the  menstrual  decidua,  but  with  this  difference,  that  the  pro- 
gressive alterations  (proliferation  of  the  connective -tissue  elements,  dila- 
tion of  the  blood-vessels  and  glands)  attain  much  greater  proportions. 
A  siipa'ficial  compact  zone  and  a  deep  spongy  zone  can  always  be  dis- 
tinguished (Fig.  280).  The  cavities  in  the  latter  are  produced  by  the 
lower  divisions  of  the  gland  tubules,  which  have  become  greatly  widened 
and  very  tortuous.      At  a  later  stage  of  pregnancy,  owing  to  the  great 


THE  REPRODUCTIVE  ORGANS. 


361 


expansion  of  the  uterus,  the  lamina  of  the  glands  appear  compressed  and 
straighter  (parallel  to  the  muscular  coat).  (Fig.  281.)  Between  the 
glands  are  numerous  blood-vessels,  spindle-cells,  and  multinucleated 
giant-cells.  The  epithelium  of  the  glands  early  begins  to  loosen,  and  in 
great  part  the  cells  lie  irregularly  scattered  in  the  lumen  of  the  tubule, 
where  they  disintegrate.  The  orifices  of  the  glands  are  gradually 
obliterated,  since  the  walls  after  the  loss  of  the  epithelium  become 
adherent  and  grow  together. 

The  blood-vessels  of  the  mucosa  are  all  dilated,  especially  the  super- 
ficial veins  and  capillaries  ;    the  latter  often  form   distended,  sinus-like 
cavities  in  the  upper  layer  of  the  decidua.      In  the  decidua   serotina  the 
arteries  and  the  veins  open  on  the  surface 
of  the  mucosa  (Fig.    283  and  Fig.  284),  so 
that  here  the  maternal  blood  circulates   be- 
tween   the    chorionic  villi  of  the    placenta 
(see  page   367).      In  the   decidua  vera  the 
blood-vessels  toward  the  end  of  pregnancy 
are  less  conspicuous. 

Of  especial  interest  are  peculiar,  t}'pi- 
cal  cells,  decidual  cells,  that  appear  in  large 
numbers  in  the  mucosa  of  the  gra\"id 
uterus.  The}'  are  flattened,  spherical,  oval, 
or  branched  cells  of  conspicuous  size  (0.03 
to  o.  I  mm.),  that  in  the  latter  half  of  preg- 
nancy assume  a  characteristic  brown  color. 
They  usualh-  possess  but  one  nucleus, 
though  occasionally  two,  three,  or  more 
are  present,  and  in  rare  cases  as  many  as 
thirty  or  forty.  The  decidual  cells  are  most  numerous  and  most  densely 
aggregated  in  the  upper  compact  zone  of  the  serotina  (Fig.  281),  which 
owes  its  typical  character  and  brown  color  to  these  elements.  Oc- 
casionally cells  are  found  that  are  united  with  one  another  by  means  of 
protoplasmic  processes.  According  to  Minot,  the  decidual  cells  originate 
from  connective-tissue  elements,  therefore  ma}'  be  regarded  as  a  modi- 
fied embryonal  or  so-called  anastomosing  connective  tissue. 

In  a  cross-section  of  the  decidua  vera  in  the  latter  half  of  pregnancy 
it  will  be  seen  that  the  surface  of  the  mucosa  is  covered  by  two  distinct 
membranes, — fetal  membranes — the  chorio?i  diWd  the  amnion  {¥\gs.  281, 
283).  The  chorion  lies  next  to  the  decidua  vera  and  is  intimately  united 
with  it.  It  consists  of  two  layers,  an  epithelial  and  a  connective-tissue 
layer,  of  which  the  former  is  turned  toward  the  uterine  wall,  the  latter 


Fig.  282. — Decidual  Cells  from  the 
Mucous  Membrane  of  a  Human 
Uterus  .^bout  Seven  Months 
Pregn.ant.  Below  a  "giant-cell," 
above  to  the  right  a  cell  with  a  kary- 
okinetic    figure.     X  250. — {Schaper.) 


362  HISTOLOGY. 

toward  the  amnion.  Two  similar  layers  may  be  distinguished  in  the 
amnion,  but  of  these  the  epithelial  layer,  which  consists  of  cubical  cells, 
is  turned  toward  the  cavity  of  the  uterus,  while  the  connective-tissue 
stratum  faces  the  chorion.  The  amnion  and  the  chorion  are  loosely 
united  to  each  other  by  mucous  connective  tissue,  in  which  delicate 
fibrils  may  be  seen  extending  from  one  membrane  to  the  other. 

The  lymph-vessels  of  the  uterus  form  in  the  mucosa  a  wide-meshed 
network  provided  with  blind  branches.  From  this  small  stems  proceed 
through  the  muscularis  and  communicate  with  a  close  subserous  network 
of  larger  channels. 

The  nerves  of  the  uterus,  medullated  as  well  as  nonmedullated,  are 
very  numerous.  They  branch — the  medullated  nerves  after  losing  their 
medullary  sheath — in  the  muscularis  and  form  a  dense  plexus  in  this 
and  in  the  mucosa.  From  the  latter  delicate  fibrils  may  be  traced 
between  the  epithelial  cells. 

The  Placenta.* 

The  placenta  is  an  organ  which  from  a  morphologic  standpoint  is 
composed  of  two  heterogeneous  parts,  of  which  the  one  is  produced  by 
the  mother  (placenta  uterina),  the  other  by  the  embryo  (placenta  foetalis). 
It  is  the  result  of  the  intimate  union  of  a  circumscribed  area  of  the  cho- 
rion (chorion  frondosum)  with  that  portion  of  the  mucosa  of  the  uterus 
known  as  the  decidua  serotina.  The  placenta  serves  the  purpose  of 
bringing  the  fetal  and  the  maternal  blood  into  the  closest  proximity,  to 
render  possible  the  interchange  of  materials  between  them.  To  subserve 
this  function  the  organ  possesses  a  peculiar  histologic  construction,  in 
which  the  blood-vessels,  especially  in  their  arrangement  and  structure, 
take  a  prominent  part. 

In  the  histologic  investigation  of  the  placenta  various  obstacles  are 
encountered,  owing  to  its  being  an  extremely  soft,  spongy  mass,  traversed 
by  numerous  wide  blood-vessels.  The  comprehension  of  the  minute 
structure  will  be  considerably  facilitated  by  proceeding  from  the  pre- 
viously mentioned  fact  that  the  finished  organ  is  the  product  of  two  origi- 
nally heterogeneous  structures,  the  chorion  on  the  one  side,  the  decidua 
serotina  on  the  other,  and  that  their  union  is  substantially  effected  in  that 
the  chorion,  by  means  of  numerous  villous-like  proliferations,  penetrates 
the  underlying  serotina,  the  surface  of  which  is  peculiarly  modified  and 
further  regressively  altered  for  its  reception,  and  as  it  were  takes  root  in 
the  same.     For  the  investigation  of  these  relations  sections  through  the 

*  This  chapter  is  an  entirely  new  addition  by  the  editor. 


THE  REPRODUCTIVE  ORGANS. 


363 


VI. 


Fig.  283. — Section  through  a  Normal  Human  Placenta  of  about  Seven  Months,  in  Situ.  Am.,  Amnion; 
Cho.,  Chorion;  Vi,  trunk  of  a  \illus;  \-i,  sections  of  \-illi  in  the  substance  of  the  placenta;  D,  decidua  basahs; 
Mc,  muscularis;  D',  compact  layer  of  decidua-.  V'e.  uterine  artery  opening  into  the  placenta.  The  fetal  blood- 
vessels are  drawn  black;  the  maternal  blood-spaces  are  left  white;  the  chorionic  tissue  is  stippled,  except  the 
canalized  fibrin,  which  is  shaded  by  lines;  the  remnants  of  the  gland  ca\ities  in  D"are  stippled  dark. — {After 
Minol.) 


'M 


HISTOLOGY. 


wall  of  the  uterus  with  the  placenta  i/i  situ,  toward  the  end  of  pregnancy, 
are  most  instructive.  In  such  a  section  two  sharply  defined  zones  may 
be  recognized :  an  outer  compact  stratum  consisting  of  the  greatly 
thickened  muscular  coat  of  the  uterus,  covered  externally  by  the  serosa, 
and  an  inner  spongy  zone  containing  numerous  inter-communicating 
spaces  filled  with  blood.  The  latter  is  the  placenta,  that  is,  the  united 
decidua  serotina  and  chorion  frondosum.  The  accompanying  illustration 
(Fig.  283)  shows  their  relations  under  low  magnification,  which  will  be 
elucidated  by  referring  to  the  schematic  representation  in  figure  284. 

The  surface  of  the  placenta  directed  toward  the  cavity  of  the  uterus 
is  covered  by  a  compact  stratum,  the  membrana  chorii,  which  is  chiefly 


Amnion 
Chorion 


Chorionic  villi. 


-J   r 

■rAy 


[     Compact 
layer. 


'y       Cavernous 
Q    |_      layer. 


Muscularis. 


^  iS^r    ^  I  ^-    Intervillous  spaces. 


Floating  villus. 

y  Attached  villi. 

Vein. 

Spiral  artery. 
Gland. 

Vein. 


Fig.  2S4. — Diagram  of  the  Human  Placenta  at  the  Close  of  Pregnancy.     Cj.  Fig.  283. — (Schaper.) 


composed  of  fibrillar  connective  tissue,  in  which  the  main  branches  of 
the  umbilical  blood-vessels  run.  The  outer  surface  of  the  chorion  is 
covered  by  a  delicate  membrane,  the  placental  portion  of  the  amnion, 
which  as  previously  stated  consists  of  an  inner  epithelial  and  a  connec- 
tive-tissue layer  and  is  attached  to  the  chorion  by  means  of  embryonic 
connective  tissue.  The  other  surface  of  the  membrana  chorii,  that 
directed  toward  the  wall  of  the  uterus,  is  closely  beset  with  innumerable 
villous-like  structures,  large  and  small,  which  in  the  upper  part  of  the 
placenta  form  a  dense  tangle,  the  terminal  ramifications  of  which  are 
embedded  in  the  cleft,  uneven  substance  of  the  serotina.  On  closer 
study  of  this  villous  tangle  it  will  be  seen  that  the  larger  stems  run  a 
more  or  less  direct  course  from  the  chorion  to  the  serotina.  in  order  to 


THE    REPRODUCTIVE    ORGANS. 


36i 


secure  a  firm  union  with  the  latter,  while  their  many  much-branched 
lateral  twigs  usually  establish  no  connection  with  the  uterine  portion  of 
the  placenta,  but  terminate  free  in  the  blood-spaces,  the  so-called  inter- 
villous spaces,  between  the  chorion  and  the  serotina.  Dependent  upon 
these  relations  the  branches  of  the  chorionic  villi  are  divided  into  roots 
of  attachment,  or  main  stems,  and  free  processes,  or  floating  villi.  From 
the  chorion  a  branch  of  the  umbilical  artery  enters  each  main  stalk  and 
within  the  terminal  ramifications  of  the  villus  breaks  up  into  a  dense 
capillary  network  from  which  the  umbilical  veins  take  their  origin  and 
carry  back  the  blood  from  the  chorion  through  the  umbilical  cord  to  the 
fetus.      Accordingly,  the  blood-vessel  system  of  the  fetal  placenta  is  entirely 


Protoplasmic  coat 
Epithelial  nucleus    -    -  -|! 
CapiUaries    <-'    -- 


Cell-knot  -- 


Small  artery. -- 


.  Cell-knot  in  process  of 
formation. 


Protoplasmic  coat  (syncytium). 


Small  \em. 


Capillary. 


Cell 


Fig.  285. — Cross-section  through  a  Smaller  (A)  and  a  Larger  (B)  Chorioxic  Villus  of  a  Human  Pla- 
centa AT  THE  End  of  Pregnancy.     X  250. — {Schaper.) 

closed.      Nowhere  does  a  direct  intermingling  of  the  maternal  arid  the  fetal 
blood  occur. 

A  cross-section  of  one  of  the  smaller  chorionic  villi,  highly  magni- 
fied, shows  that  it  is  chiefly  composed  of  mesenchymal  tissue  (mucous 
tissue),  in  which  the  blood-vessels  are  embedded  (Fig.  285).  This 
central  supporting  substance  is  covered  by  an  irregular  and  not  every- 
where continuous  stratum  of  epithelium.  In  the  earlier  months  of  devel- 
opment two  distinct  strata  may  be  distinguished  in  the  epithelium  of  the 
viUi  :  an  inner,  lying  immediately  upon  the  supporting  tissue,  in  which 
the  cells  possess  large  nuclei  and  definite  contours,  so  that  in  the  main 
they  are  distinctly  separated  from  one  another,  and  an  outer  layer,  con- 
sisting of  a  continuous  protoplasmic  mass — syncytium — containing  num- 


366  '  HISTOLOGY. 

erous  small,  irregularly  scattered  nuclei.  Toward  the  end  of  pregnancy, 
however,  the  epithelium  of  the  villi  undergoes  great  alteration,  as 
appears  in  the  illustration  (Fig.  285).  On  the  larger  villi  a  true  epithe- 
lial investment  has  almost  entirely  disappeared  and  instead  isolated 
accumulations  of  large  round  nuclei  are  found  ;  they  stain  intensely,  are 
embedded  in  a  clear,  homogeneous  substance,  and  form  protuberances 
{Zellknoten,  cell-knots)  on  the  surface  of  the  villi.  Between  these  cell- 
knots  the  connective-tissue  of  the  villi  frequently  is  covered  only  by  a 
thin,  homogeneous  stratum,  or  in  some  cases  (especially  in  smaller  villi) 
this  stratum  still  retains  more  or  less  the  character  of  the  protoplasm 
containing  scattered  nuclei.  There  are  many  indications  that  the  latter 
is  the  remains  of  the  syncytium,  while  the  cell-knots  probably  origi- 
nated in  the  primitive  inner  stratum  of  the  epithelium  of  the  villi.*  In 
many  places  the  syncytium  is  transformed  into  a  peculiar  hyaline  sub- 
stance permeated  by  fissures,  which  often  lies  upon  the  chorion  in  dense 
strata  and  is  called  canalized  fibrin. 

The  histologic  structure  of  the  maternal  portion  of  the  placenta — 
placenta  titerina — in  its  essential  features  has  been  described  in  connec- 
tion with  the  decidua  in  the  preceding  chapter.  But  certain  peculiarities, 
as  well  as  the  union  of  maternal  and  fetal  placenta  in  a  functional  whole, 
require  a  brief  consideration. 

The  placental  portion  of  the  decidua  (Fig.  283),  that  forming  the 
lower  stratum  of  the  placenta  (basal  plate),  is  greatly  thinned  (from  0.5 
to  I  mm.),  but  as  in  the  extraplacental  portion  an  upper  compact  layer 
and  a  lower  cavernous  layer  (gland  lumina)  may  be  distinguished.  The 
decidual  cells  are  extremely  numerous  and  lie  closely  crowded.  A 
honeycomb  structure  of  connective-tissue  septa  {septa  placentce)  arises 
from  the  surface  of  the  serotina,  directed  toward  the  intervillous  spaces, 
and  penetrates  between  the  villi  of  the  chorion,  separating  the  latter  into 
lobes  or  cotyledons.  Only  in  the  peripheral  regions  of  the  placenta  do 
these  septa  reach  to  the  membrana  chorii,  where  frequently  they  form  on 
the  inferior  surface  of  the  latter  a  thin  membranous  stratum,  the  decidua 
placentalis  snbclwrialis.  On  the  margin  of  the  placenta  the  serotina 
gradually  increases  in  thickness  and  passes  into  the  vera,  at  which  point 
it  is  closely  applied  to  and  firmly  united  with  the  chorion.      Within  the 

*  It  has  not  been  yet  determined  with  certainty  whether  the  epithelium  of  the  villi  of  the 
Iiuman  placenta  is  entirely  derived  from  the  epithelium  of  the  chorion,  or  whether  the  epi- 
thelium of  the  serotina  participates  in  its  composition.  However,  recent  investigations  as  well 
as  comparative  anatomical  facts  indicate  that  only  the  inner  epithelial  stratum  of  the  villi  comes 
from  the  chorionic  epithelium,  while  the  syncytium  is  derived  directly  from  the  mucosa  of  the 
uterus,  the  epithelium  of  which,  on  the  ingrowth  of  the  chorial  villi,  becomes  closely  applied 
to  and  blends  with  the  epithelium  of  the  latter. 


THE  REPRODUCTIVE  ORGANS.  367 

area  of  the  placenta,  however,  the  chorion  and  the  serotina  are  far  apart 
and  the  space  between  them  is  filled  with  the  above-described  chorial 
villi  and  the  blood  circulating  between  them  ;  it  is  maternal  blood  that 
surrounds  the  villi  on  all  sides  and  is  thus  brought  into  the  closest 
relation  with  the  fetal  circulation. 

Of  especial  interest  is  the  behavior  of  the  blood-vessels  within  the 
placenta  uterina  (Fig.  283  and  Fig.  284).  Numerous  arteries  from  the 
muscularis  of  the  uterus  penetrate  the  serotina,  in  which  they  make  cork- 
screw-like tours  during  the  course  of  which  they  lose  their  muscular  coat 
and  continue  as  wide  tubes  consisting  alone  of  the  lining  epithelium. 
Near  the  surface  of  the  decidua  they  usually  bend  sharply  at  right  angles 
and  then  open  directly  into  the  intervillous  spaces  of  the  placenta.* 
Nozuhere  do  the  arteries  break  up  into  capillaries.  The  veins  (likewise 
epithelial  tubes,  though  wider  than  the  arteries)  also  are  in  direct  com- 
munication with  the  placental  spaces  ;  they  enter  the  decidua  usually 
under  a  very  narrow  angle,  run  more  or  less  parallel  to  the  surface,  and 
unite  in  the  deeper  strata  in  a  wide  venous  plexus.  In  accordance  with 
the  description  of  these  conditions  of  the  vessels  the  arteries  and  the 
veins  within  the  serotina  can  no  longer  be  recognized  by  the  histologic 
structure  of  their  walls,  but  can  be  distinguished  only  by  their  width  and 
their  course.  In  addition  the  arteries  usually  are  characterized  by  a 
thin,  homogeneous,  enveloping  stratum  that  stains  intensely  with  car- 
mine, in  which  a  few  scattered  nuclei  are  found.  This  peculiar  layer  is 
probably  a  product  of  the  degenerated  muscular  coat. 

The  umbilical  cord  of  the  fetus  at  term  consists  of  the  umbilical  vessels, 
two  arteries  and  a  vein,  with  somewhat  thinner  walls,  which  are  held  together 

*In  regard  to  the  relation  of  the  decidual  blood-vessels  to  the  intervillous  spaces  there  are 
two  conflicting  theories.  According  to  the  one  the  intervillous  spaces  are  independent  clefts 
without  proper  walls,  that  are  formed  in  the  course  of  development  between  the  fetal  and 
maternal  portions  of  the  placenta,  with  which  the  blood-vessels  opening  on  the  surface  of 
the  decidua  are  in  direct  communication.  Accordingly  the  villi  of  the  chorion  are  in  direct 
contact  with  the  maternal  blood  circulating  in  these  spaces.  The  opposite  view  regards  the 
blood-spaces  of  the  placenta  as  the  enormously  widened  capillaries  of  the  decidua,  which,  dur- 
ing the  mutual  process  of  intergrowth  between  the  placenta  uterina  and  the  placenta  fcetalis,  the 
developing  villi  of  the  chorion  have  invaginated.  According  to  this  the  blood-vessel  system  of 
the  decidua  is  closed  and  the  arteries  and  the  veins  communicate  through  a  system  of  capillary 
lacunae  (the  intervillous  spaces).  Further,  the  chorial  villi  are  not  directly  bathed  in  the 
maternal  blood,  but  are  separated  from  it  by  a  thin  stratum  of  cells,  the  capillary  epithelium, 
which  lies  directly  upon  them.  Recent  investigations  of  Keibel  apparently  support  the  latter 
view,  since  in  a  human  placenta  in  an  early  stage  of  development  he  succeeded  in  tracing  the 
epithelium  of  the  decidual  blood-vessels  into  the  intervillous  spaces  and  demonstrating  it  as  a 
continuous  stratum  on  the  surface  of  the  chorionic  villi.  It  is  possible  that  in  the  further  de- 
velopment of  the  placenta  this  epithelial  covering  undergoes  regressive  change,  so  that  in  later 
stages  it  cannot  as  a  rule  be  demonstrated. 


368  HISTOLOGY. 

by  Wharton  s  Jelly.  The  latter  is  a  mixture  of  gelatinous  connective  tissue 
and  connective-tissue  strands,  usually  running  longitudinally,  often  united  net- 
fashion.  These  vessels  are  richly  provided  with  transverse  and  longitudinal 
smooth  muscle-fibers,  between  which  a  delicate  connective  tissue  is  found,  that 
for  the  greater  part  is  united  in  small,  perforated  membranes  and  forms  a  sack- 
like sheath  (not  a  sarcolemma)  around  each  muscle-fiber,  which  under  the  influ- 
ence of  hardening  and  staining  reagents  gives  rise  to  the  deceptive  appearance 
of  intercellular  bridges.  More  or  less  large  remnants  of  the  allantois  are  found 
in  the  umbilical  cord,  a  strand  about  o.i  mm.  broad,  formed  of  epithelial 
cells.  A  simple  or  stratified  squamous  epithelium,  developed  from  the 
amnion,  covers  the  surface  of  the  umbilical  cord.  Smaller  blood-vessels, 
nerves,  and  lymph-vessels  are  wanting  in  the  matured  umbilical  cord,  but  the 
jelly  is  penetrated  by  a  network  of  juice-canals  (p.  100). 

The  Vagina  and  the  External  Female  Genitalia, 

The  vagina  is  formed  of  a  mucoids  membrane,  a  muscle  membrane, 
and  a  fibrous  membrane. 

The  vmcoiis  vienibrane  is  composed  of  (i)  a  stratified  squamous 
epithelium  and  (2)  a  tunica  propria  beset  with  papillae,  built  up  of  small, 
interlacing  bundles  of  connective  tissue,  and  containing  a  few  elastic 
fibers  and  a  varying  quantity  of  leucocytes.  The  latter  occasionally 
exist  in  the  form  of  solitary  nodules  ;  in  this  case  numerous  migrating 
leucocytes  are  found  arrested  in  the  epithelium  in  these  localities.  The 
deepest  layer  of  the  mucosa  is  formed  by  (3)  a  subimicosa,  which  is  com- 
posed of  loosely  united  connective-tissue  bundles  and  robust  elastic 
fibers.      Glands  are  absent  in  the  vaginal  mucous  membrane. 

The  vmsadar  membrane  comprises  an  inner  circular  and  an  outer 
longitudinal  layer  of  smooth  muscle-fibers. 

The  outer  fibrous  membrane  is  a  dense  connective-tissue  structure, 
rich  in  elastic  fibers. 

The  blood-  and  lymph-vessels  are  arranged  in  parallel  horizontal  net- 
works in  the  submucosa  and  in  the  tunica  propria.  Between  the  bundles 
of  the  muscular  membrane  lies  a  close  network  of  wide  veins.  The 
nerves  form  a  plexus  in  the  outer  fibrous  tunic,  beset  with  many  small 
ganglia. 

The  mucous  membrane  of  the  external  female  genitalia  in  the 
vicinity  of  the  clitoris  and  the  urethral  meatus  differs  from  the  vaginal 
mucosa  in  the  possession  of  numerous  mucous  glands,  from  0.5  to 
3  mm.  in  size,  and  on  the  labia  minora  sebaceous  glands  *  (without 
hair-follicles)  from  0.2  to  2  mm.  in  size  are  found.  The  clitoris  repeats 
on  a  diminutive  scale  the  structure  of  the  penis  ;  tactile  corpuscles  and 
genital  nerve  corpuscles  occur  in  the  glans  clitoridis. 

*  They  are  wanting  at  birth  and  are  not  distinct  until  the  fifth  year. 


THE  REPRODUCTIVE  ORGANS.  369 

The  large  glands  of  the  vestibule  (Bartholini)  are  the  homologues  of 
the  bulbourethral  glands  in  the  male. 

The  labia  majora  possess  the  same  structure  as  the  external  skin. 

The  acid  vaginal  mucus  contains  desquamated  squamous  epithelial 
cells  and  leucocytes,  and  not  infrequently  an  infusorium,  the  trichomonas 
vaginalis. 

TECHNIC. 

No.  144. — For  a  general  viezv  of  the  testis  make  a  transverse  in- 
cision *  through  the  testis  and  the  epididymis  of  a  newborn  child  ;  f  fix 
both  pieces  in  about  50  c.c.  of  potassium-bichromate  acetic  acid  (p.  32) 
and  harden  in  30  c.c.  of  gradually  strengthened  alcohols  (p.  35).  Stain 
thick  transverse  sections  of  the  entire  organ  with  Hansen's  hematoxylin 
and  dilute  eosin  (p.  39),  and  mount  in  xylol-balsam.  Examine  with 
very  low  powers  (Fig.  258). 

No.  145. — Minute  structure  of  the  seminiferous  tubules. — Place 
small  pieces  (2  cm.  cubes)  of  the  fresh  testis  of  an  ox  in  200  c.c.  of 
Zenker's  fluid  (p.  33),  and  harden  them  in  50  c.c.  of  gradually  strength- 
ened alcohols  (p.  35).  Cut  the  sections  as  thin  as  possible,  stain  them 
with  Hansen's  hematoxylin  (p.  38),  and  mount  in  xylol-balsam. 

No.  146. — Still  better  preparations  are  obtained  by  placing  the  entire 
testis  of  a  mouse  ;{:  in  10  c.c.  of  the  platinum-acetic- 
osmic  acid  mixture  (p.  34)  for  twenty-four  hours  for 
fixation,  washing  it  for  several  hours  in  running-  water, 
and  hardening  it  in  20  c.c.  of  gradually  strengthened 
alcohols.  Mount  the  unstained  sections  in  xylol- 
balsam  (Fig.  262). 

No.  147. — Elements  of  the  testis. — Place  pieces 
about  I  c.c.  in  size  of  the  fresh  testis  of  an  ox  in 
20  c.c.  of  one-third  alcohol  (p.  20)  and  in  five  or  six  _ 

hours  tease  the  content  of  the  tubules  in  a  drop  of  Elements  of  the 

the  same  alcohol.      Stain  under  the  cover-glass  with  X240.  a.cMother- 

picrocarmine  (p.    53)  and    mount    in   dilute  glycerol.  bias't'.'*'rf,!mm"m?; 

Several  preparations  from  different  parts  of  the  organ  m^tSe  ^emeT'fiia- 

should  be  completed  ;  then  not  infrequently  the  cells  ""en'- 

of  Sertoli  with  attached  spermatocytes,  or  the  semen 
filaments  produced  by  them,  will  be   obtained  (Fig.  286,  b),   structures 
that  formerly  were  described  as  "  spermatoblasts." 

*  In  the  testis  of  the  rabbit,  cat,  and  dog  the  mediastinum  is  not  at  the  margin,  but  in 
the  interior  of  the  organ. 

t  If  no  incision  is  made  into  the  organ  it  does  not  harden  sufficiently,  because  the  dense 
tunica  albuginea  retards  the  penetration  of  the  fluids. 

i  The  platinum-chlorid   mixture  does  not  fully  penetrate  the   testes  of  larger  animals ; 
only  the  peripheral  portions  can  be  used. 
24 


--"ViL 


370  HISTOLOGY. 

No.  148. — Elements  of  the  semen. — Make  an  incision  into  a  fresh 
epididymis  *  and  place  one  drop  of  the  milk-white  fluid  that  escapes 
from  the  cut  surface  on  a  clean  slide  ;  add  one  drop  of  salt  solution, 
apply  a  cover-glass,  and  examine  with  the  high  power.  Often  the  semen 
filaments  are  not  active  ;  a  gentle  warming  of  the  slide  over  the  flame 
of  a  spirit-lamp  will  quickly  call  forth  their  motility.  After  a  time  let 
one  drop  of  distilled  water  flow  under  the  cover-glass  ;  the  movements 
soon  cease  ;  the  heads  of  the  majority  of  the  semen  filaments  then  pre- 
sent their  broad  surface  and  the  tail  curves  and  forms  a  loop  (Fig.  263,  3). 
Remnants  of  protoplasm  still  adhere  to  semen  filaments  not  fully 
matured.  The  filaments  can  be  preserved  by  diluting  the  semen  with  a 
drop  of  distilled  water  containing  ammonia  (5  c.c.  distilled  water  -f-  i  drop 
ammonia)  and  allowing  it  to  dry  on  the  slide  ;  apply  a  coverglass  and 
fasten  with  cement  (p.  50).  In  such  preparations  too  much  illumination 
gives  rise  to  troublesome  reflexes.     ' 

No.  149. — The  stability  of  the  semen  filaments  permits  investiga- 
tions for  forensic  purposes.  For  example,  it  may  be  a  question  as  to 
whether  spots  occurring  on  a  linen  garment  were  caused  by  semen.  Cut 
strips  2  to  10  mm.  square  from  suspected  stiff  spots,  soak  them  for  from 
five  to  ten  minutes  in  a  watch-glass  containing  distilled  water,  and  tease 
a  few  fibers.  With  a  high  power  (500  :  i)  chiefly  examine  the  edges  of 
the  isolated  linen  fibers,  to  which  the  semen  filaments  if  present  are 
attached.  Not  infrequently  the  heads  are  broken  off;  they  are  recog- 
nized by  their  peculiar  luster,  their  shape,  and  their  (in  man  small)  size. 

No.  150. — Semen  filaments  of  tlie  frog. — The  male  frog  is  recog- 
nized by  a  well-developed  wart  on  the  ball  of  the  thumbs.  Open  the 
abdominal  cavity  ;  the  testes  are  a  pair  of  oval  bodies  (resembling  the 
kidneys  of  mammals)  lying  to  either  side  of  the  vertebral  column.  Divide 
the  organ  by  a  transverse  incision  ;  dilute  a  drop  of  the  contained  fluid 
with  a  drop  of  salt  solution.  The  filaments  are  large,  the  head  thin  and 
elongated,  the  tail  so  delicate  that  at  first  glance  it  may  be  overlooked. 
Immature  filaments  lie  grouped  in  tufts. 

No.  151. — Epididymis,  ductus  deferens,  and  seminal  vesicle. — Fix 
pieces  from  i  to  2  cm.  in  size  in  about  100  c.c.  of  Zenker's  fluid  (p.  33) 
and  harden  them  in  60  c.c.  of  gradually  strengthened  alcohols.  Stain 
the  sections  with  Hansen's  hematoxylin  and  mount  in  xylol-balsam  (Fig. 
264-267). 

No.  I  52. — The  prostate  and  the  different  divisions  of  the  male  urethra 
are  to  be  prepared  in   2  or  3  cm.  cubes  like  No.   151   (Fig.   268,  269). 

No.  153. — TJie  ovary. — The  ovaries  of  small  animals  may  be  fixed 
in  toto,  those  of  larger  animals  and  of  man  with  several  incisions  trans- 

*  For  a  view  of  the  spiral  fiber  mentioned  above  (p.  341,  remark*),  that  can  be  seen  only 
with  immersion  lenses,  I  recommend  the  seminal  filaments  of  the  rat ;  they  are  to  be  examined 
in  water. 


THE    REPRODUCTIVE    ORGANS.  37 1 

verse  to  the  long  axis,  in  100  or  200  c.c.  of  Zenker's  fluid  (p.  33)  and 
hardened  in  100  c.c.  of  gradually  strengthened  alcohols  (p.  35).  For  a 
topographic  view  (Fig.  270)  it  is  advisable  to  cut  thick  sections,  because 
otherwise  the  contents  of  the  follicles  easily  fall  out.  Not  every  section 
includes  large  follicles ;  it  is  often  necessary  to  cut  many  sections  in 
order  to  hit  a  favorable  place.  Human  ovaries  have  a  very  thick  tunica 
albuginea  (Fig.  287)  and  furnish  less  satisfactory  preparations  than  animal 
ovaries.  Stain  the  sections  with  Hansen's  hematoxylin  (p.  38).  Mount 
in  xylol-balsam. 

No.  I  54. — Fresh  cgg-cclls  may  be  obtained  as  follows.  Procure  the 
fresh  ovaries  of  a  cow.  The  large  vesicular  follicles  are  transparent,  pea- 
sized  vesicles,  which  with  the  scissors  can  be  easily  shelled  out  in  toto. 
Transfer  an   isolated  follicle  to  a  slide  and  prick  it  with  a  needle.      The 


m. 


Primitive  follicles.        -■.■.•:^  .  i^  ■^r^rs^^r'-, 
'^■'^ 

B. 

Fig.  287. — A.  Section  of  an  Ovary  of  a  Girl  17  Years  Old.     X  3.     X  is  the  portion  shown  in  B.     B, 

tunica  albuginea.     X  120. 

needle  must  be  carefully  thrust  in  on  the  side  of  the  follicle  lying  against 
the  slide,  otherwise  the  liquor  will  spurt  out  and  carry  the  egg  with  it. 

The  egg,  surrounded  by  the  cells  of  the  cumulus  oophorus,  escapes 
with  the  liquor  folliculi  and  must  be  searched  for  in  the  uncovered  prep- 
aration with  a  low  power  (Fig.  274  Ay  If  it  is  desired  to  examine  the 
egg  with  high  powers  place  on  each  side  of  it  a  strip  of  thin  paper  and 
cover  it  with  a  cover-glass. 

The  beginner  will  sacrifice  many  a  follicle  before  he  succeeds  in 
finding  an  egg.  Often  the  egg  does  not  escape  when  the  follicle  is 
pricked  ;  it  may  then  be  found  by  teasing  the  follicle. 

No.  155. — Egg's  of  the  frog. — Place  a  small  piece  of  the  fresh  ovary 
of  a  frog  on  a  slide  and  prick  all  the  large  pigmented  eggs,  so  that  their 
contents    escape.       Place   that  which  remains  in  a  watch-glass  with   dis- 


3/2  •  HISTOLOGY. 

tilled  water  and  wash  by  moving  it  to  and  fro  with  needles.  Place  the 
watch-glass  on  a  black  background  ;  the  smaller,  still  unpigmented  folli- 
cles can  then  be  seen.  Transfer  the  washed  object  to  a  clean. slide,  apply 
a  cover-glass,  and  examine  it.  The  eggs  have  very  large  germinal  vesi- 
cles ;  the  germinal  spot  disappears  early  and  usually  is  not  to  be  seen. 
On  the  other  hand,  a  dark  spot  occurs  in  the  vitellus,  the  "  nucleus  of 
the  vitellus,"  which  corresponds  to  the  archoplasm  (p.  65).  Encircling 
the  egg  is  a  finely  striated  membrane,  the  inner  surface  of  which  is 
covered  with  flat  cells  ;  this  is  the  theca  folliculi  with  the  simple  follicular 
epithelium. 

No.  156. —  T/ie  oviducts. — Fix  pieces  i  or  2  cm.  long  in  50  c.c.  of 
Miiller's  fluid  and  harden  them  in  60  c.c.  of  gradually  strengthened  alco- 
hols (pp.  33,  35).  Stain  with  Hansen's  hematoxylin  and  mount  in 
xylol-balsam.      (Fig.  276.) 

No.  1 57. — Topographic  preparations  of  the  human  ntertis. — Fix  2  cm. 
cubes  in  100  c.c.  of  the  Miiller-formol  mixture  (p.  33)  and  harden  them  in 
100  c.c.  of  gradually  strengthened  alcohols  (p.  35).  Stain  in  Hansen's 
hematoxylin  and  in  eosin  (p.  39)  and  mount  in  xylol-balsam  (p.  50). 
(Fig.  277.)  In  the  two-horned  uteri  of  many  animals  the  often  greatly 
convoluted  gland  tubules  can  be  more  readily  distinguished ;  the  arrange- 
ment of  the  muscular  strata  is  different,  more  regular  than  in  the  human 
organ. 

No.  158. — For  preparations  of  the  human  uterine  mucosa,  the  fresh, 
living  tissue  obtained  at  surgical  operations  should  be  put  into  the  fixing 
reagent.  Cut  pieces  i  cm.  square  and  treat  them  after  No.  157.  Owing 
to  the  extreme  tortuousness  of  the  glands  sections  contain  only  frag- 
ments of  them.     The  cilia  can  seldom  be  seen  in  fixed  preparations. 

No.  159. — The  placenta  is  to  be  treated  according  to  No.  158.* 
Before  cutting  sections  the  pieces  must  be  embedded  in  celloidin  or  in 
paraffin ;  in  the  latter  case  the  sections  must  be  fastened  to  the  slide  (see 
Microtome  Technic),  in  order  that  the  innumerable  branches  of  the  villi, 
cut  in  every  plane,  do  not  fall  out.  The  study  of  preparations  of  this 
kind  is  one  of  the  most  difficult  tasks  of  the  microscopist. 

No.  160. — The  umbilical  cord.      Prepare  like  No.  4,  p.  loi. 
*  Fixation  in  absolute  alcohol  often  yields  very  good  results. 


THE    SKIN. 


373 


IX.   THE   SKIN. 

The  external  skin  {integiime^itiim  coDinmne,  cutis)  in  its  chief  mass 
consists  of  connective  tissue,  which  however  is  nowhere  exposed,  but  is 
protected  by  a  continuous  epithelial  cover.  The  connective-tissue  por- 
tion of  the  skin  is  called  coriuni  or  derma,  the  epithelial  portion,  epidermis. 
The  appendages  of  the  skin,  the  nails  zn^  the  Jiairs,  as  well  as  the  glands 
and  the  hair -follicles  embedded  within  the  depths  of  the  corium,  are 
products  of  the  epidermis. 


Epi- 
dermis. 


Stratum  corneum. 


Stratum  lucidum. 
Stratum  germinativum. 


Stratum  papillare. 
Corium.  J  Excretory  duct. 

Stratum  reticulare. 

Coil-gland. 

Stratum  subcutaneum. 


Fig.  288. — Vertical  Section  of  the  Skin  of  the  Finger  of  Adult  Man.     X  25.    With  this' magnification 
the  stratum  granulosum  is  not  visible.     Technic  No.  161. 


The  External  Skin. 

The  corium. — The  surface  of  the  corium  is  marked  by  many  fine 
furrows,  which  intersect  and  bound  rectangular  or  lozenge -shaped  fields 
or  run  parallel  for  longer  stretches  between  minute  ridges.  The  lozenge- 
shaped  fields  may  be  seen  on  the  surface  of  the  greater  part  of  the  body, 
while  the  ridges  are  confined  to  the  volar  surface  of  the  hand  and  the 
plantar  surface  of  the  foot.  These  fields  and  ridges  are  beset  with 
numerous  conical  elevations,  the  papillce,  the  number  and  size  of  which 
vary  greatly  in  different  regions  of  the  body.  The  largest  (up  to  0.2 
mm.  high)  and  most  numerous  papillae  occur  on  the  palm  of  the  hand 
and  on  the  sole  of  the  foot ;  they  are  very  slightly  developed  in  the 
skin  of  the  face. 

The  corium  chiefly  consists  of  netlike  interlacing  connective-tissue 


374  •       HISTOLOGY. 

bundles,  mingled  with  elastic  fibers,  cells,  and  smooth  muscle-fibers.  In 
the  superficial  layers  of  the  corium  the  connective-tissue  bundles  are  deli- 
cate and  are  united  in  a  closely  interwoven  texture  ;  in  the  deeper  layers 
they  are  larger  and,  intersecting  at  acute  angles,  form  a  coarse-meshed 
network.  These  differences  have  led  to  the  recognition  of  two  strata  in 
the  corium,  a  superficial  stratum  beset  with  papillae,  the  stratum  papillare, 
and  a  deep  stratum,  the  stratum  reticulare.  There  is  no  sharp  demarca- 
tion between  the  two  strata,  the  one  gradually  blending  with  the  other 
(Fig.  288).  The  stratum  reticulare  is  connected  with  an  underlying 
network  of  loosely  united  bundles  of  connective  tissue,  the  wide  meshes 
of  which  contain  clusters  of  fat-cells  ;  this  is  the  stratum  subciitaneum. 
The  storing  of  much  adipose  tissue  in  the  interfascicular  spaces  of  this 
stratum  leads  to  the  formation  of  thf?  panniculus  adiposus.  The  bundles 
of  the  subcutaneous  stratum  are  firmly  or  loosely  connected  with  the 
connective-tissue  sheaths  of  the  muscles  (the  fasciae)  or  of  the  bones  (the 
periosteum).  The  elastic  fibers,  which  are  thin  in  the  stratum  papillare 
and  thicker  in  the  stratum  reticulare,  form  networks  *  uniformly  distrib- 

3  Depressions  which  were 

occupied  by  papillae. 


Furrow  corresponding  to 
a  ridge  of  the  corium. 


Portion  of  the  duct  of  a 
coil-gland. 


Fig.  289. — Epidermis  from  the  Skin  of  the  Dorsum  of  the  Human  Foot,  seen  from  the  Lower  Surface 
X  120.  The  preparation  is  so  to  speak  the  cast,  while  the  surface  of  the  corium  beset  with  papillae  repre- 
sents the  matrix.    Technic  No.  162. 

uted  throughout  the  corium.  The  easily  shifted  membrane  of  subcu- 
taneous tissue  is  relatively  poor  in  elastic  fibers  ;  particularly  rich  in 
these  is  the  skin  of  the  face  and  of  the  vicinity  of  the  joints.  The  cells 
include  spindle-shaped  and  plate-like  connective-tissue  elements,  leuco- 

*  Recent  authors  distinguish  four  layers  of  elastic  fibers:  (l)  a  layer  consisting  of 
numerous  thick  elastic  fibers,  that  lies  immediately  above  the  common  fascia  of  the  body;  (2) 
a  zone  in  the  stratum  reticulare,  here  the  fibers  run  with  the  blood-vessels ;  (3)  a  dense  sub- 
papillary  plexus  and  (4)  a  sub-epithelial  network.  The  first  three  layers  are  freely  connected. 
In  old  age  a  notable  disappearance  of  elastic  fibers  occurs. 


THE    SKIN.  375 

cytes,  and  fat-cells.  The  number  of  the  cellular  elements  is  extremely 
variable.  The  vinsclc-fibcrs  almost  exclusively  belong  to  the  nonstriped 
variety  and  the  majority  are  attached  to  the  hair-follicles  (p.  379) ;  only 
in  a  few  situations  in  the  body  do  they  occur  as  membranous  expansions 
in  the  skin  (tunica  dartos,*  nipple).  Striated  muscle-fibers  occur  in  the 
skin  of  the  face,  where  they  radiate  from  the  mimetic  muscles. 

TJic  epidermis. — The  epidermis  consists  of  a  stratified  squamous 
epithelium,  in  which  at  least  two  sharply  defined  zones  can  be  distin- 
guished :  a  deep  zone,  the  germinal  stratum,  stratum  germinativum 
(Malpighi),  which  fills  the  depressions  occurring  between  the  papillse  of 


Part  of  the  stratum 
corneum. 


Stratum  lucidum. 
Stratum  granulosum. 


Q      -^                                  ^        ^*              ".^ 

^®           -         '.                      ..     ^     .-    -?-j 

Stratum  germinativum. 
-  Part  of  the  papillary  laver 

of  the  corium. 

Fig.  290. — From  a  Section  through  the  Skin  of  the  Sole  of  the  Foot  of  Adult  Man.     X  360.    Technic 

No.  161. 

the  corium,  and  a  superficial,  firmer  zone,  the  horny  stratum,  stratiim 
corneinn.  Both  strata  consist  exclusively  of  epithelial  cells,  which  exhibit 
different  appearances  in  the  separate  layers.  In  the  deepest  layer  of  the 
stratujii  germitiativum  the  cells  are  membraneless,  cylindrical,  and  possess 
oblong  nuclei ;  these  are  followed  by  several  layers  of  spherical  cells 
that  are  beset  with  numerous  delicate  thorns  and  are  named  prickle-cells. 
The  thorns  are  delicate,  thread-like  processes,  which  serve  to   connect 

*  Here  the  muscle-fibers  are  profusely  interlaced  with  elastic  fibers. 


3/6  HISTOLOGY. 

neighboring  cells  to  one  another.  Therefore  they  are  called  intercellu- 
lar bridges  (Fig.  23,  p.  79).  In  the  stratum  germinativum  new  cells 
are  continually  being  formed  by  indirect  nuclear  division.  The  stratum 
corneuin  is  not  everywhere  of  the  same  structure  and  two  different  types 
may  be  distinguished:  (i)  In  localities  where  the  epidermis  is  thick, 
as  on  the  palm  of  the  hand  and  the  sole  of  the  foot,  a  stratum 
of  cells  characterized  by  highly  refracting  granules  *  (keratohyaline 
granules)  lies  next  to  the  stratum  germinativum.  The  granules  are  a 
decomposition  product  of  the  interfilar  mass  and  the  stratum  is  named 
the  stratum  granulosum  (Fig.  290).  These  granules  liquefy  and  form  a 
diffuse  mass,  the  eleidin,  that  saturates  the  cells  and  produces  a  glisten- 
ing, homogeneous  stratum,  the  stratiun  lucidjun.  This  is  covered  by  the 
broad  stratum  corneum  proper.  Here  the  eleidin  has  become  firmer 
(pareleidin),t  the  exoplasm  of  the  cells  is  transformed  into  a  horny  mem- 
brane, the  protoplasm  in  the  interior  of  the  cells  is  desiccated  and  forms  a 
delicate  meshwork  ;  the  intercellular  bridges  are  no  longer  connecting 
threads,  but  are  short,  small  teeth.  The  nucleus  is  desiccated  ;  but  the 
cavity  which  it  occupied  persists  for  a  long  time.  These  partly  cornified, 
partly  desiccated  cells  are  only  slightly  flattened.  (2)  In  situations  where 
the  epidermis  is  thinner  (all  the  remaining  surface  of  the  skin),  the 
stratum  granulosum  is  narrow  and  interrupted  by  gaps.  The  stratum 
lucidum  is  absent.  The  cells  of  the  stratum  corneum,  enveloped  in  a 
horny  membrane,  are  extremely  flattened  and  are  united  in  lamellae. 
The  last  trace  of  the  nucleus  is  lost. 

The  surface  of  the  stratum  corneum  is  subject  to  a  constant  desquam- 
ation ;  the  resulting  loss  is  compensated  by  the  pushing  upward  of  the 
elements  of  the  germinal  stratum. 

The  color  of  the  skin  is  due  to  the  deposition  of  fine  granules  of 
pigment  between  and  within  the  cells  of  the  deeper  layers  of  the  epider- 
mis ;  only  in  certain  localities,  for  example,  in  the  vicinity  of  the  anus, 
are  pigmented  connective-tissue  cells  found  in  the  adjacent  corium. 

With  regard  to  the  source  of  the  pigment  of  the  epidermis  there  are 
two  theories,  of  which  the  one  attributes  its  origin  to  the  connective 
tissue,  the  other  to  the  epithelium.  According  to  the  first,  hitherto 
widely   accepted  opinion,   the   so-called    "  transportation "    theory,    the 

*  These  granules  dissolve  in  a  solution  of  potassium  hydroxid,  therefore  do  not  consist 
of  keratin,  which  is  insoluble  in  this  reagent. 

•j"  The  pareleidin  blackens  like  fat,  but  only  after  the  prolonged  action  of  osmic  acid  ; 
therefore  the  black  staining  of  the  horny  cells  of  thick  epidermis  cannot  be  attributed  to  the 
saturation  of  the  stratum  corneum  with  fat  from  the  exterior,  derived  from  the  secretion  of 
the  sebaceous  or  coil-glands. 


THE    SKIN. 


377 


pigment  is  carried  to  the  epithelium  by  pigmented  connective-tissue  cells, 
that  wander  from  the  corium  into  the  epidermis  and  there  disintegrate. 
In  the  human  hair-bulb  pigmented  forms  presenting  great  diversity  in 
outline  are  actually  found  between  the  epithelial  elements  ;  some  of  these 
figures  are  cells,  but  it  has  not  been  demonstrated  with  certainty  that 
they  are  connective-tissue  cells,  others  are  not  cells,  but  intercellular 
clefts  filled  with  pigment.  The  second  theory  is  supported  by  the  de- 
velopmental history,  which  teaches  that  the  pigment  originates  in  the 
epithelium  of  the  hair  without  the  intervention  of  connective-tissue  cells. 
The  pigment  of  the  retina  also  is  certainly  and  exclusively  of  epithelial 
origin. 

The  Nails. 
The  nails  are  horny  laminae,  which  rest  upon  a  special  modification 
of  the  skin,  the  nail-bed.     The  nail-bed  is  bounded  laterally  by  the  nail- 


NaU- 
*'«<^-j    Epithe 


Eponychium. 


Fig.  291. — Dorsal  Half  of  a  Cross-section  of  the  Third  Phalanx  of  a  Child.     X  is-    The  ridges  of  the 
nail-bed  in  cross-section  appear  Uke  papilla.     Technic  No.  163. 


walls,  a  pair  of  sloping  folds  with  the  descent  forward.  The  nail-bed 
and  nail-wall  embrace  a  furrow,  the  nail-groove,  in  which  the  lateral 
border  of  the  nail  is  inserted  (Fig.  291).  The  posterior  border  of  the 
nail,  the  nail-root,  rests  in  a  similar  but  deeper  groove  ;  here  the 
principal  growth  of  the  nail  takes  place  ;  this  place  is  named  the  matrix.'^ 
The  anterior  free  border  of  the  nail  projects  over  the  nail-ridge,  a  small, 
seam-like  prominence  at  the  distal  end  of  the  nail-bed. 

The  nail-bed  coxxsists  of  corium  and  of  epitheUum.  The  connective- 
tissue  bundles  of  the  corium  contain  many  elastic  fibers  and  are  partly 
disposed  parallel  to  the.  long  axis  of  the  finger,  partly  run  vertically  from 
the  periosteum  of  the  phalanx  to  the  surface.  The  surface  of  the  corium 
does  not  possess  papillae,  but  minute  longitudinal  ridges.     They  begin 

*  Other  authors  name  the  whole  nail-bed  matrix, which  is  in  a  measure  justified  by  the 
growth  in  the  thickness  of  the  nail  that  occurs  here. 


3/8  HISTOLOGY. 

low  at  the  matrix,  increase  in  height  toward  the  anterior  border  of  the  nail 
and  terminate  abruptly  at  the  point  where  the  latter  leaves  its  bed.  The 
epithelium  is  of  the  stratified  squamous  variety,  of  the  same  structure  as 
that  of  the  germinal  stratum  of  the  epidermis.  It  covers  the  ridges  of 
the  nail-bed,  fills  up  the  furrows  between  them,  and  is  sharply  defined 
from  the  substance  of  the  nail.  The  matrix  likewise  consists  of  corium 
and  of  epithelium  ;  the  corium  is  distinguished  by  its  tall  papillae,  the 
stratified  squamous  epithelium  is  very  thick  and  is 
not  sharply  defined  from  the  nail-substance,  but 
gradually  blends  with  it.  This  is  .the  place  where  by 
continual  division  of  the  epithelial  cells  the  material 
for  the  growth  of  the  nail  is  furnished.  On  this  ac- 
count the  epithelium  is  here  called  the  genn-layer  of 
the  nail.  The  extent  of  the  matrix  is  indicated  by  the 
^'°'a  Hu^AN^:^fL^^  X  l^tnula,  a  white,  anteriorly  convex  field,  visible  to  the 
240.  Technic  No.  unaided  eye ;  it  is  produced  by  the  thick,  uniformly 
extended  germ-layer.  The  nail-wall  exhibits  the 
usual  structure  of  the  skin.  The  germinal  stratum  of  the  same  gradu- 
ally blends  with  the  epithelium  of  the  nail-bed  ;  the  horny  stratum  ex- 
tends into  the  nail-groove  and  as  "eponychium"  covers  a  small  portion 
of  the  border  of  the  nail,  but  soon  diminishes  in  thickness  and  disap- 
pears (Fig.  291). 

The  nail  itself  consists  of  horny  epithelial  scales,  that  are  very 
firmly  united  with  one  another  and  are  distinguished  from  the  horny 
cells  of  the  stratum  corneum  of  the  epidermis  by  the  possession  of  a 
nucleus  (Fig.  292).* 

The  Hairs  and  the  Hair-follicles. 

The  hairs  are  flexible,  elastic,  horny  threads,  which  are  distributed 
over  nesLrly  the  entire  surface  of  the  body  and  on  the  integument  of  the 
cranium  are  united  in  small  groups.  The  part  of  the  hair  which  projects 
beyond  the  free  surface  of  the  skin  is  called  the  shaft  [scapns)  ;  the  por- 
tion obliquely  embedded  within  the  skin  is  named  the  root  {I'adix pili)  ; 
this  at  its  lower  extremity  is  expanded  to  a  hollow  knob,  the  hair-bulb 
{bulbus pili^,  which  is  occupied  by  a  formation  of  the  corium,  the  hair- 
papilla  (Fig.  293). 

Each  hair-root  is  inserted  in  the  hair-follicle,  a  modification  of  the 

*  The  new  anatomic  nomenclature  reckons  the  epithelium  of  the  nail-bed  to  the  nail, 
that  according  to  this  representation  consists  of  two  layers,  the  stratum  corneum  and  the 
stratum  germinativum. 


THE    SKIN. 


379 


skin  in  the  construction  of  which  the  corium  and  the  epidermis  partici- 
pate ;  the  parts  furnished  by  the  latter  are  named  the  cpitliclial  root-sheatlis  ; 
the  portion  originating  from  the  corium  is  named  the  dermal  or  connec- 
tive-tissue hair-follicle.  From  two  to  five  glands,  the  sebaceous  glands, 
open  laterally  into  the  upper  part  of  the  follicle.  Bundles  of  smooth 
muscle-fibers,  the  arrectores  pilornni,  provided  with  elastic  tendons  at  the 
point  of  origin,  pass  obliquely  down  from  the  upper  surface  of  the  corium 
and  attach  themselves  beneath  a  sebaceous  gland  to  the  connective- 
tissue  hair-follicle  ;  the  point  of  insertion  of  these  fibers  is  always  on 
the  side  toward  which  the  hair  inclines  and  forms  an  acute  angle  with 
the  free  surface  of  the  skin  ;  consequently  when  they  contract  the  follicle 


Hair-shaft. 

Hair-root. 
Sebaceous  gland. 

Arrector  pili  muscle. 


Root-sheaths. 
Coanective-tissue  follicle. 

Hair-bulb. 

Hair-papilla. 

Fat-cells.  . — '  "^^   \ 

Fig.  293. — From  a  Thick  Section  of  the  Human  Scalp.     X  20.    Technic  No.  168. 

and  the  shaft  become  erect.  The  arrector  muscles  are  wanting  on  the 
lanugo  hairs  of  the  nose,  the  cheeks,  the  lips,  also  on  the  cilia  and  the 
vibrissae. 

The  hair  consists  entirely  of  epithelial  cells,  which  are  arranged  in 
three  well-defined  strata  :  (i)  the  cuticle,  which  covers  the  surface  of  the 
hair  ;  (2)  the  cortical  substance,  which  forms  the  chief  bulk  of  the  hair  ; 
(3)  the  medulla,  which  occupies  the  axis  of  the  hair. 

The  cuticle  (cuticula  pili)  consists  of  transparent,  imbricated  scales  : 
horny,  nonnucleated  epithelial  cells. 

The  cortical  substance  of  the  shaft  consists  of  slender,  horny  epi- 
thelial  cells   provided  with   thin,   linear-shaped  nuclei,   which   are  very 


38o 


HISTOLOGY. 


intimately  united  with  one  another ;  on  the  root  the  cells  become  softer 
and  rounder,  their  nucleus  correspondingly  more  spherical,  the  nearer 
they  lie  to  the  hair-bulb. 

The  medulla  is  absent  in  many  hairs  ;  when  it  is  present  (in  the 
thicker  hairs)  it  does  not  extend  through  the  entire  length  of  the  hair. 
It  consists  of  cubical  epithelial  cells  containing  keratohyaline  granules 
(P-  375).  which  enclose  a  rudimentary  nucleus  and  are  usually  disposed 
in  twofold  rows  beside  one  another. 

The  colored  hairs  contain  pigment,  in  solution  and  in  the  form  of 
granules,  which  partly  occur  between  and  partly  within  the  cells  of  the 


Cortical  sub- 
stance. 


Medullary  sub- 
stance. 


Cuticle. 


■^lr;ti"Lip 


Fig.  294. — Elements  of  a  Human  Hair  and  Hair-Follicle.  X  240.  i.  White  hair;  2,  scales  of  the  cuticle; 
3,  cells  of  the  cortical  substance  of  the  shaft;  4,  cells  of  Huxley's  layer;  s,  cells  of  Henle's  layer,  having  the 
appearance  of  a  fenestrated  membrane;  6,  cells  of  the  cortical  substance  of  the  root.  Technics  No.  166  and 
No.  167. 

cortical  substance.*  In  every  hair  which  has  attained  its  full  develop- 
ment extremely  minute  air  vesicles  occur  ;  they  are  found  in  the  cortical 
substance  as  well  as  in  the  medulla,  in  the  intercellular  spaces. 

The  follicle  of  finer  (lanugo)  hairs  is  formed  alone  by  the  epidermal 
root-sheaths,  but  in  coarser  hairs  the  corium  participates  in  its  construction. 
In  the  follicles  of  the  latter  the  following  strata  are  distinguished  :  an 
outermost  longitudinal  fiber-lay  er,'\  formed  of  vascular,  loose  connective- 


*  Regarding  the  source  of  the  pigment,  see  page  376. 

f  Elastic  fibers  occur  only  in  the  longitudinal  fiber-layer  ;  in  the  ring  fiber-layer  and  in  the 
papilla  they  are  wanting. 


THE    SKIN. 


381 


tissue  bundles,  richly  supplied  with  nerves  ;  following  this  is  a  thicker 
layer  of  circularly  arranged,  delicate  connective-tissue  bundles,  the  ring 
fiber  layer,  which  is  contiguous  to  an  inner  clear,  transparent  membrane, 
the  hyaline  membrane.  These  three  strata  are  derived  from  the  corium  * 
and  together  are  named  the  connective-tissue  hair-follicle  ;  it  is  to  be  seen 
in  complete  development  only  in  the  lower  half  of  the  entire  hair-follicle. 
Within  the  hyaline  membrane  lies  the  outer  root-sheath,  which  as  the  con- 
tinuation of  the  germ-layer  of  the  epidermis  consists  of  stratified  squamous 
epithelium  ;  inward  to  this  lie  continuations  of  the  stratum  granulosum  and 
stratum  corneum,  which  latter  extends  to  the  point  where  the  ducts  of  the 
sebaceous  glands  open  into  the  follicle,  while  the  former  extends  a  little 


i?^. 


j    Longitudinal   fiber- 
layer. 
Connective-      \    t,-      £u      1 
tissue  follicle.    \   R^ng  fiber-layer. 


Inner  root- 
sheath. 


(_  Hyaline  membrane.  ^~7^    f 

Outer  root  sheath.    '~f'\- 

C  Henle's  layer.  - — \'i' 


Huxley's  layer. 

(  Sheath  and  hair  cuticu- 
te. 


Hair.  J    Cortical  substance. 


Medullary  substance. 


•it- 


'     ,'4/ 


Fig.  295. — From  a  Horizontal   Section   of  the  Human  Scalp.     X  240.     Cross-section  of  a  hair  and  hair- 
follicle  in  the  lower  half  of  the  root.     Technic  No.  168. 

farther  downward;  immediately  beneath  (toward  the  papilla)  the  imier 
root-sheath  begins  abruptly,  which  in  the  lower  portion  of  the  follicle  is  dif- 
ferentiated into  two  sharply  defined  layers.  The  outer  of  these  two,  Henle's 
layer,  consists  of  a  single  or  double  row  of  nonnucleated  epithelial  cells 
(here  and  there  an  atrophic  nucleus  is  present),  while  the  inner,  Huxley's 
layer,  is  formed  of  a  simple  stratum  of  nucleated  cells.  The  inner  sur- 
face of  this  layer  is  lined  with  a  delicate  membrane,  the  cuticle  of  the  root- 
sheath,  which  exhibits  the  same  structure  as  the  cuticle  of  the  hair. 
Toward  the  base  of  the  follicle  the  outer  root-sheath  diminishes  in  thick- 
ness and  at  the  neck  of  the  hair-papilla  it  disappears  ;  there  its  elements 


*  The  inner  portion  of  the  hyaline  membrane  is  said  to  be  of  epithelial  origin. 


382 


HISTOLOGY, 


Hair-cuticle.     Cortical  substance. 
<         I 


Hair. 


Medullary  substance. 


%    <^^ 


Longitudinal 
fiber-layer 


Ring  fiber-layer    - 


Connective-tis 
sue  follicle 


1'%%  fi|  ^  >"\^      8*1  /  ->-s  if    *|  '"t<  1      fl       ,^  lis 


Outer  root 
sheath. 


Henle's  layer 
Huxley's  layer 


1 


^AJ*: 


Hair-papilla 


Fig.  296. — Longitudinal  Section  of  the  Lowest  Division  of  the  Root  of  a  Hair;  the  keratohyaline  gran- 
ules are  colored  red.     From  a  vertical  section  of  the  human  scalp.     X  200.     Technic  No.  168. 


THE    SKIN.  383 

are  drawn  sharply  into  a  transx^erse  position  and  in  tangential  longitudinal 
sections  of  the  root-sheath  hav^e  the  appearance  of  short,  circular  smooth 
muscle-fibers.  The  elements  of  the  inner  root-sheath  and  of  the  cuticulae 
all  become  nucleated  cells,  that  can  be  distinguished  as  separate  layers 
until  near  the  neck  of  the  papilla ;  there  they  lose  their  sharp  demarca- 
tion, but  nevertheless  can  be  distinguished  from  the  cells  of  the  hair- 
bulb  by  the  pigmentation  of  the  latter.*  The  hair-papilla  is  covered  with 
a  thin,  distinctly  double-contoured  continuation  of  the  hyaline  mem- 
brane. 

The  Development  of  the  Hairs. 
The  first  anlage  of  the  hair  appears  at  the  end  of  the  third  embry- 
onal month  and  at  first  in  the  form  of  a  local  thickening  of  the  epidermis, 
which  is  caused  by  elongation  of  the  deepest  cells  of  the  epidermis  and 
by  multiplication  of  the  cells  of  the  middle  layers  (Fig.  297).  This  liair- 
germ  (Fig.  298)  grows  in  length,  down  into  the  corium,  and  becomes  a 

.  Cells  of  the 

Hair-genn.  hair-canal.  Hair-germ.     Terminal  bar. 


-  --■»:.      -  •um       -m  -  ^    ~~        r  Epidermis. 


./^/T. 
-z^ 


w—'H 


'*  'i^^—f^^^ 


Corium.  _ .       •      Vl^'S*^ 

Fig.  297. — Vertical  Section  of  the  Skin  of  the  Abdomen        Fig.  298. — Vertical  Section  of  the  Skin  of 
OF  A  Human  Fetus  of  Five  Months.    X  230.   Technic  the  Back  of  a  Human  Fetus  of  Five 

Xo.  169.  Months.     X  230.    Technic  No.  169. 

solid  epithelial  peg,  the  hair-peg,  at  the  blind  end  of  which  a  thicker 
aggregation  of  connective-tissue  cells,  the  anlage  of  the  hair-papilla,  has 
developed  (Fig.  299)  ;  a  second  accumulation  of  cellular  elements  of  the 
corium,  appearing  at  the  under  side  of  the  hair-peg,  is  the  anlage  of  the 
arrector  muscle  (Fig.  300).  The  lower  end  of  the  hair-peg  grows  around 
the  papilla,  converting  the  entire  anlage  into  the  bulb-peg,  which  develops 
two  evaginations,  an  upper,  the  future  hair-follicle  gland,  and  a  lower,  the 
future  hair-matrix  (Fig.  301). 

The  epithelial  cells  of  the  bulb-peg  lying  next  to  the  papilla  develop 
into  the  hair-cone  (Fig.  302),  while  the  remaining  epithelial  cells  develop 
into  the   outer  root-sheath.     The  hair-cone  grows  in  length,  its  periph- 


*  Already  at  the  level  of  the  papilla  keratohyaline  granules  appear  in  the  cells  of  Henle's 
layer,  at  a  somewhat  higher  level  also  in  those  of  Huxley's  layer  (Fig.  296),  that  a  little  farther 
up  disappear  ;  from  this  upward  the  elements  of  the  inner  root-sheath  are  corneous. 


'M 


HISTOLOGY. 


eral  cells  become  the  inner  root-sheath  (Fig.  303),  its  axial  cells  become 
the  hair,  while  the  epithelial  cells  lying  between  these  produce  the 
cuticulae    of   the   sheath    and   the  hair.      In  this    staee   the  entire   hair. 


Hair-peg. 


Cells  of  the  hair-canal. 


Hair- peg. 


Anlage  of  arrec- 
tor  muscle. 


Anlage  of  papilla. 


Fig.  299. — Vertical  Section  of  the  Skin  of  the 
Back  of  a  Human  Fetus  of  Five  Months. 
X  230.     Technic  No.  169. 


Anlage  of  papilla. 

Fig.  300. — Vertical  Section  of  the  Skin  of  the 
Flexor  Side  of  the  Thigh  of  a  Human  Fetus 
of  Five  Months.    X  230.   Technic  No.  169. 


Tangential  section  of  a  hair-germ. 


Cells  of  the  hair-canal. 

r 


Anlage  of  the  gland  of  the  hair-foUicle. 


Anlage  of   the   hair-matrix. 


Fig.  301. — Vertical  Section  of  the  Skin  of  the  Gluteal  Region  of  a  Human  Fetus  of  Five  Months. 
Transition  of  the  Hair-peg  into  the  Bulb-peg.     X  230.    Technic  No.  169. 


including  its  tip,  is  completely  enclosed  in  the  inner  root-sheath,  gradu- 
ally becoming  horny  from  above  downwards.  This  is  the  stage  of  the 
slieathed  hair  (Fig.  304). 


Outer 

root-sheath 


Tangential  section 
of  a  hair-peg. 


Tip  of 

hair-cone. 


Tangential  section  of 
the  anhme  of  a 
hair-follicle  gland.  ■ 


Hyahne 

membrane, 


I'ndifferentiated 
'cells  of  the 
(hair-cone. 


^^ Papilla. 


Fig.  302. — Bulb-peg.  From  a  Vertical  Section 
OF  THE  Bridge  of  the  Nose  of  a  Human 
Fetus  of  Seven  and  a  Half  Months. 
X  230.     Technic  No.  169. 


Hair-matrix. 


Hyaline  membrane. 
Papilla. 


Fio.  303. — Sheathed  Hair.  Vertical  Section  of 
the  Skin  of  the  Back  of  a  Human  Fetus  of 
Five  AND  a  Half  Months.  \  230.  Technic 
No.  169. 


Tangential  section  of  the  outer  root-sheath 
Horny  inner  root-sheath. 


♦  % 


Arrector  muscle. 


Fig.  30J.— Vertical  Section  of  the  Skin  of  the  Forehead  of  a  Human  Fetus  of  Five  Months.  X  230- 
Differentiation  of  the  sheaths  of  the  hair.  Above  the  point  of  the  tangential  section  ot  the  outer  root-sheath 
the  degenerating  end  of  the  inner  root-sheath  is  seen  projecting  into  the  smaU  portion  of  the  hair-canal  m- 
duded  in  the  section.     Technic  No.  169. 


25 


385 


386 


HISTOLOGY. 


Hair-matrix. 


^1    ,         Outer  root-sheath. 


Meanwhile  the  axial  cells  in  the  upper  division  of  the  hair-peg  * 
grow  horny  and  perish  and  give  rise  to  a  horizontal  canal  in  the  epidermis, 
the  hair-canal  (Fig.  305),  which  is  closed  toward  the  free  surface  ;  the 

inner  root-sheath  gradu- 

Blood-vessel.  Hair-canal.  ^JJ^    mOVCS    Up    intO    the 

hair-canal  and  perishes 
there,  so  that  the  tip 
of  the  hair,  now  also 
horny,  projects  free  out 
of  the  inner  root-sheath. 
This  is  followed  by  the 
breaking  through  of  the 
hair  and  the  opening  of 
the  hair-canal  on  the 
free  surface ;  the  inner 
root-sheath  now  reaches 
only  up  to  the  open- 
ing of  the  hair-follicle 
glands.  Meanwhile  the 
hyaline   membrane,   the 

Fig.  305.— Vertical  Section  of  the  Skin  of  the  Back  of  a  Human  ring  and  longitudinal 
Fetus  of  Five  and  a  Half  Months.    X  120.    The  staining  with               °                               ° 

.    iron-hematoxyhn  has  made  the  horny  parts  so    black    that   their  fiber  layers  haVC    dcvcl- 

fc  details  are  invisible.    Technic  No.  169.  •'^ 

oped  from  the  connec- 
tive-tissue bulb-peg,  so  that  the  newly  escaped  hair  possesses  all  the 
parts  of  the  fully  developed  hair. 

Hairs  may  originate  in  the  manner  described  after  birth,  up  to  old 
age. 

GROWTH    OF    THE    HAIR    AND    OF    THE    ROOT-SHEATHS. 

The  growth^  of  the  hair,  of  the  inner  root-sheath,  and  of  its 
cuticula  takes  place  by  continual  mitotic  division  of  the  epithelial  ele- 
ments at  the  bulbus  pili,  the  matrix  cells,  that  become  horny  and  annex 
themselves  from  below  to  previously  cornified  cells.  Therefore  the  tip 
is  the  oldest,  the  portion  lying  immediately  above  the  hair-bulb  the 
youngest  part  of  the  hair.  The  outer  root-sheath,  on  the  other  hand, 
grows  in  a  radial  direction  from  the  inner  surface  of  the  hyaline  mem- 
brane towards  the  axis  of  the  hair. 


THE    SHEDDING    AND    RENEWAL    OF    HAIR. 

Shortly  before  and  after  birth  a  total  exchange  of  hair  takes  place 


*  The  differentiation  of  these  cells  of  the  hair-canal  begins  very  early  {cf.  Fig.  2c 


THE    SKIN. 


387 


and  also  in  adult  man  a  constant,  but  not  periodic  renewal  occurs,  to 
replace  the  shed  hairs  of  the  head  and  beard.*  In  this  process  the 
hollow  hair-bulb  ("  hollow  root ")  is  transformed  into  a  solid,  horny  bulb 
("solid  root"),  that  is  lifted  from  the  papilla  and  crowded  up  under  the 
opening  of  the  sebaceous  glands  and  then  falls  out ;  meanwhile  a  new 
hair  originates  on  the  papilla. 

The  minuter  processes  are  as  follows  :  the  ring  fiber-layer  and  the  hyaline 
membrane  grow  thicker  and  the  matrix  cells  cease  to  divide,  those  of  the  inner 
root-sheath  first,  while  tho§e  of  the  hair  itself  continue  to  produce  for  a  time 


Bulb-hair. 

Epithelial  cord. 
Hair-papilla. 


Hair-follicle  gland. 


.«•■■.       /.-^  . .  .^  —     Bulb-hair  (club-hair). 

Epithelial  cord. 


Hair-papUIa. 
Fig.  306. — From  a  Vertical  Section  of  the  Scalp  of  Adult  Man.    X  40-    Technic  No.  170. 


and  then  also  cease  their  activity.  In  this  way  the  lower  end  of  the  hair  becomes 
transformed  to  a  bulb,  which  gradually  removes  from  the  hair-papilla,  that  is 
still  covered  with  a  few  matrix  cells. 

These  matrix  cells  multiply,  however,  without  becoming  elements  of  the 
hair  or  sheaths,  grow  larger  and  with  the  aid  of  the  thickened  ring  fiber-layer 
and  the  now  multiplying  epithelial  cells  of  the  outer  root-sheath  push  the  hair 
up  to  the  level  of  the  attachment  of  the  arrector  muscle.  At  this  locality,  of  the 
hair-matrix  ("  bulb  site  "),  the  bulb-hair  f  (club-hair),  having  meanwhile  be- 
come completely  horny,  remains  for  a  time,  ceases  to  grow,  and  later  falls  out. 


*  The  duration  of  life  of  a  scalp  hair  is  said  to  be  1600  days.  Regarding  the  shedding 
and  renewal  of  the  other  hairs  definite  knowledge  is  wanting. 

t  With  the  ascent  of  the  bulb-hair  the  inner  root-sheath,  that  extends  only  up  to  the  open- 
ing of  the  sebaceous  glands,  for  the  greater  part  is  lost. 


388 


HISTOLOGY. 


The  small  epithelial  cord  situated  under  the  hair-matrix  becomes  greatly  short- 
ened and  pulls  up  the  now  atrophic  hair-papilla,  altered  in  shape,  while  the 
strata  of  the  connective-tissue  hair-follicle  remain  and  form  the  hair-stalk. 
After  a  time  the  elements  of  the  epithelial  cord  are  regenerated  from  the 
cylinder-cell  layer  of  the  hair  matrix  ;  the  cord  extends  down  to  the  old  papilla ; 
new  matrix  cells  produce  a  young  hair,  in  the  mode  previously  described  for  the 
first  development  of  hairs,  that  gradually  moves  obliquely  into  the  original 
depth,  and  with  its  tip  next  to  the  bulb-hair,  which  later  falls  out,  it  pushes 
upward  to  the  surface. 

The  Glands  of  the  Skin. 
The  hair-follicle  glands  (sebaceous  glands,  glandulse  sebaceae)  are 
either  unbranched  or  branched  alveolar  simple  glands.  Each  gland 
consists  of  a  short  excretory  duct  (Fig.  307  A,  a)  and  of  a  gland  body 
formed  of  a  varying  number  of  little  sacks  {t).  The  excretory  duct  is 
clothed  by  an  extension  of  the  outer  root-sheath,  therefore  with  stratified 
squamous  epithelium,  which  by  a  gradual  decrease  of  its  layers  passes 
into  the  epithelium  of  the  gland  body.      Externally  this  consists  of  low, 


\ 


Epidermis. 


Corium. 


-4«<^ 


'^   Cell  with  shrunken 
nucleus. 


'■'  CeU  with  well-devel- 
oped drops  of  secre- 
tion. 


\^\    2    Cell  with  developing 


drops  of  secretion. 
Cubical  cell. 


Fig.  307. — A.  From  a  Vertical  Section  through  the  Ala  Nasi  of  a  Child.  X  40.  C.  Stratum  comeum; 
M,  stratum  germinativum;  /,  sebaceous  gland  consisting  of  four  sacks,  a,  duct  of  the  same;  w,  lanugo  hair, 
about  to  be  shed,  h,  hair-foUicle  of  the  same,  at  the  base  of  which  a  new  hair,  x,  is  forming. 

B.  From  a  Vertical  Section  of  the  Skin  of  the  Ala  Nasi  of  an  Infant.  X  240.  Sack  of  a  sebaceous 
gland  containing  gland-cells  in  various  stages  of  secretion.     Technic  No.  171. 


cubical  cells  {B) ;  within  these  lie  spherical  or  polygonal  cells,  varying 
in  size,  which  fill  the  entire  gland-sack  and  exhibit  all  the  transitional 
phases  in  the  process  by  which  the  cell  is  converted  into  the  secretory 
product  of  the  gland.  The  secretion,  the  sebum,  during  life  is  a  semi- 
fluid substance,  that  consists  of  fat  and  disintegrated  cells.  While  the 
.sebaceous  glands  occur  as  appendages  of  the  hair-follicles  of  the  coarser 
hairs  (Fig.  293),  in  the  case  of  the  lanugo  hairs  reversed  relations  pre- 
vail, since  the  follicles  of  the  latter  appear  as  the  appendages  of  the 
powerfully   developed   sebaceous   glands  (Fig.  307  A).      The  sebaceous 


THE    SKIN.  389 

glands  are  distributed  with  the  hairs  over  the  entire  body  and  are  wanting 
only  where  they  are  absent,  on  the  palm  of  the  hand  and  on  the  sole  of 
the  foot.  There  also  are  sebaceous  glands  that  are  not  associated  with 
hair-follicles  ;  for  example,  on  the  red  edge  of  the  lips,  on  the  labia 
minora,  on  the  glans,  on  the  prasputium  penis  ;  in  the  latter  situation 
they  are  known  as  glanduUr  pnnpntiales.^'  The  sebaceous  glands  are 
always  situated  in  the  superficial  layers  of  the  corium,  in  the  stratum 
papillare.  Their  size  varies  from  0.2  to  2.2  mm.;  the  latter  are  found 
in  the  skin  of  the  nose,  where  their  excretory  ducts  are  visible  to  the 
unaided  eye. 

The  coil-glaiids  (sweat  glands,  glandulae  sudoriparae)  are  long, 
unbranched  tubules,  that  at  their  lower  end  are  rolled  into  a  spherical 
coil,  having  a  diameter  of  0.3  to  7  mm.  (of  the  latter  size  in  the  axilla). 
Two  parts  are  distinguished,  the  excretory  duct  and  the  coil  (Fig.  288). 
The  duct  runs  a  straight  or  sinuous  course  through  the  corium,  enters 
between  two  papillae  into  the  epidermis,  in  the  stratum  corneum  of  which 
it  is  spirally  twisted,  and  opens  on  the  surface  of  the  skin  by  a 
rounded  lumen,  the  siveat-porc ,  just  visible  to  the  naked  eye.  The  wall 
of  the  excretory  duct  consists  of  longitudinally  disposed  bundles  of  con- 
nective tissue  and  within  this  of  a  double  layer  of  cubical  epithelial 
cells.  The  coil  is  a  much  convoluted  single  f  canal,  the  wall  of  which  is 
formed  of  a  simple  layer  of  cubical  cells,  containing  granules  of  pigment 
and  of  fat ;  external  to  this  is  a  delicate  membrana  propria.  Inter- 
cellular and  intracellular  secretory  capillaries  occur  in  the  coil-glands. 
In  well-developed  glands  longitudinally  disposed  smooth  muscle-fibers 
occur  between  the  membrana  propria  and  the  gland-cells. 

The  secretion  usually  is  a  fatty  substance,  for  the  purpose  of  lubri- 
cating the  skin  ;  only  under  the  influence  of  disturbed  innervation  do 
the  coil -glands  discharge  the  watery  liquid  called  sweat.  Destruction 
of  the  gland-cells  does  not  occur  either  in  the  one  or  the  other  mode  of 
secretion.  The  coil-glands  are  distributed  over  the  entire  surface  of  the 
skin  and  are  absent  only  on  the  glans  penis  and  on  the  inner  surface  of 
the  prepuce.  They  are  most  numerous  in  the  skin  of  the  palm  of  the 
hand  and  of  the  sole  of  the  foot. 

*  They  may  be  wholly  wanting ;  to  name  them  Tyson's  glands  is  incorrect,  because 
under  this  designation  Tyson  described  depressions  in  the  superficial  epithelium,  crypts  regu- 
larly present,  from  j^  to  i  cm.  long,  chiefly  in  the  form  of  a  flat  pocket,  occurring  in  the  neigh- 
borhood of  the  frenulum  prseputii.  Preputial  glands,  as  well  as  crypts,  are  wanting  in  the 
glans  and  pra^putium  clitoridis.  In  the  fetus  the  inner  surface  of  the  prseputium  and  the  outer 
surface  of  the  glans  are  united  by  a  solid  epithelial  mass,  that  often  does  not  break  up  until  after 
birth,  through  the  formation  of  concentrically  stratified  epithelial  pearls. 

f  Branched  tubules  have  been  observed  only  in  the  axillary  and  circumanal  coil-glands. 


390 


HISTOLOGY, 


The  Blood-vessels,   Lymph-vessels,  and  Nerves  of  the  Skin. 

The  arteries  of  the  skin  originate  in  a  network  lying  above  the  fascise 
and  branch  as  they  ascend  toward  the  surface  of  the  skin.  These  branches 
anastomose  with  one  another  and  with  those  of  neighboring  arteries  and 
in  the  lower  stratum  of  the  corium  form  a  horizontally  disposed  reticu- 
lum, the  cutaneous  netzvork.  The  arteries  supplying  the  skin  are  there- 
fore not  end-arteries.* 

From  this  network  two  capillary  territories  are  supplied  ;  the  deeper 
is  intended  for  the  adipose  tissue  (Fig.   308,  a'),  the  more  superficial 


I  ^^      l  Epidermis. 


Corium. 


Stratum  subcutaneum. 


Fig.  308. — From  a  Vertical  Section  of  the  Skin  of  the  Sole  of  a  Human  Foot.  X  so.  sc.  Stratum  cor- 
neum;  sg,  stratum  germinativum ;  a,  artery;  v,  vein;  a',  v' ,  their  branches  to  the  panniculus  adiposus; 
a",  ?/',  their  branches  to  the  coil-glands;  a'",  v'",  their  branches  to  the  papillae;  k,  coU-gland;  ki,  duct  of 
thesame;  vx,  vein  accompanying  the  duct.     Technic  No.  172. 

appears  in  the  form  of  basket-like  plexuses  surrounding  the  coil-glands 
{a").  From  the  cutaneous  network  twigs  ascend  that  anastomose  and 
form  a  second  horizontal  network  in  the  upper  third  of  the  corium,  the 
subpapillary  plexiLS ;  from  this  very  small  twigs  arise,  which  run  for  a 


*"  End-arteries  "  are  those  small  arteries  which  do  not  anastomose  with  neighboring 
arteries,  but  independently  supply  capillary  circuits  of  varying  extent.  When  they  become 
obstructed  the  part  of  the  organ  which  they  supply  dies. 


THE    SKIN. 


391 


short  distance  along  the  rows  of  papillae  and  send  little  branches  into 
them  (Fig.  308,  a'").  These  smallest  twigs  do  not  anastomose  with  one 
another,  hence  are  end-arteries.  The  branches  intended  for  the  hair- 
follicles  and  the  sebaceous  glands  also  arise  from  the  subpapillary  plexus. 

The  blood  returning  from  the  capillary  vessels  of  the  papillae,  the 
hair-follicles,  and  the  sebaceous  glands  is  taken  up  by  veins  that  form  a 
horizontal  plexus  lying  close  beneath  the  papillae  and  that  occasionally  are 
united  with  a  second  horizontal  plexus  lying  very  close  below  the  first. 
From  this  plexus  small  venous  trunks  descend  beside  the  arteries  and  lead 
to  a  third  network  lying  in  the  lower  half  of  the  corium,  which  is  not  so 
horizontally  spread  out  as  its  predecessors.  This  plexus  takes  up  the 
veins  coming  from  the  coil-glands  and  then  those  proceeding  from  the 
lobules  of  adipose  tissue.  It  should  further  be  noted  that  a  branch  ot 
the  veins  of  the  coil-glands  passes  along  the  excretory  duct  to  the  venous 
plexus  of  the  stratum  papillare  (Fig.  308,  v  x)  and  that  the  hair-papilla 
receives  an  independent  arterial  branch.  From  the  third  venous  network 
larger  veins  lead  to  the  lower  boundary  of  the  skin,  where  a  fourth 
horizontally  disposed,  "subcutaneous"  venous  network  occurs,  from 
which  larger  stems  turn  into  the  subcutaneous  stratum  and  then  unite  with 
the  large  subcutaneous  veins,  some  of  which  are  provided  with  names. 

The  lymph-vessels  form  two  horizontal  capillary  networks,  of  which 
that  consisting  of  smaller  tubules  and  narrower  meshes  lies  in  the 
papillary  stratum  of  the  corium  beneath  the  blood  vascular  network  ;  the 
other,  wider-meshed,  is  situated  in  the  subcutaneous  stratum.  Special 
networks  of  lymph  capillaries  surround  the  hair-follicles,  the  sebaceous 
and  the  coil-glands. 

The  nerves  of  the  integument  (very  numerous  in  the  palm  of  the 
hand  and  the  sole  of  the  foot)  partly  end  in  the  subcutaneous  stratum  in 
lamellar  corpuscles  (p.  222)  ;  partly  in  terminal  cylinders  (p.  226),  that 
occur  in  the  stratum  subcutaneum  in  the  vicinity  of  the  body  of  the  coil- 
glands,  also  in  the  corium  of  the  toe  and  finger  pads;  partly  they  find 
their  ending  in  tactile  corpuscles,  in  tactile  cells,  as  free  ramifications  in 
the  papillae  with  vascular  loops,  and  as  intraepithelial  fibers  (Fig.  145). 
The  hairs  also  are  supplied  with  medullated  nerve-fibers,  which  run  up  to 
the  point  where  the  sebaceous  glands  open  into  hair-follicles  ;  here  they 
divide,  lose  their  medullary  sheath,  and  as  naked  axis-cylinders,  usually 
running  longitudinally,  terminate  in  a  spoon-shaped  expansion  on  the 
hyaline  membrane  (epilemmal  nerve-ending) ;  in  the  tactile-hairs  (sensory 
hairs)  of  animals  delicate  twigs  arise  from  these  nerves,  which  pass 
through  the  hyaline  membrane  of  the  hair-follicle  into  the  outer  root- 
sheath  and  there  end  in  tactile  disks  (p.  221),     The  hair-papilla  does  not 


392  HISTOLOGY. 

possess  nerves.     The  nerves  of  the  coil-glands  behave  similarly  to  those 
of  the  glands  of  the  oral  cavity  {cf.  p.  247). 

The  Mammary  Gland. 

The  mammary  gland,  a  convoluted  alveolo-tubular  compound 
gland,  in  children  of  both  sexes  consists  chiefly  of  connective  tissue, 
which  encloses  the  branched  excretory  gland-ducts.  These  ducts  have 
a  bulbous  enlargement  at  their  termination.  End-pieces  are  wanting. 
The  mammary  gland  of  the  adult  male  exhibits  the  same  structure. 

In  the  adult  female  the  mammary  gland  up  to  the  occurrence  of 


Branch  of  an  excretory  duct.  Connective  tissue 


Tubule. 


Alveolo-tubule, 


*&■; 


Fig.  309. — Section  of  a  Human  Mammary  Gland  at  the  Period  of  Lactation.    X  so-    Technic  No.  174, 

pregnancy  is  a  disk-shaped  body,  that  consists  chiefly  of  connective 
tissue  and  of  the  excretory  gland-ducts.  End-pieces  are  present  only 
in  limited  number  at  the  ends  of  the  smallest  branches  of  the  excretory 
ducts. 

At  the  time  of  pregnancy  and  of  lactation  the  mammary  gland  con- 
sists of  from  fifteen  to  twenty  alveolo-tubular  compound  glands,  which 
are  held  together  and  united  in  a  common  body  by  loose  connective 
tissue  containing  fat-cells.  Each  of  these  glands  has  its  own  excretory 
duct  opening  on  the  nipple,  that  shortly  before  its  termination  is  provided 
with  a  conspicuous  spindle-shaped  expansion,  the  milk-sack  or  ampulla 


THE    SKIN.  393 

[sinus  lactifcrus)  and  by  means  of  dichotomous  ramifications  is  connected 
with  the  end-pieces.  The  latter  lie  close  beside  one  another  and  are 
bound  together  by  connective  tissue  into  small  lobules. 

Touching  the  microscopic  structure,  the  excretory  ducts  consist  of 
a  cylinder  epithelium,*  followed  outside  by  a  membrana  propria  and  con- 
nective-tissue bundles  chiefly  having  a  circular  arrangement. 

The  end-pieces  differ  in  structure  during  the  period  of  gestation  and 
during  the  period  of  lactation.      During  gestation  the    end-pieces    are 
clothed  with  a  simple    cubical  or  somewhat 
flattened    epithelium  ;     their    lumen    contains 
leucocytes  that  have  wandered  in  from  the  un- 
derlying interstitial  connective-tissue  through 
the    epithelium.      Some    of  these    leucocytes 
perish  (their  nucleus  is  ragged,  often  divided 
into   several   pieces),  the  others   take   up   fat 
drops  furnished  by  the  gland-cells  and  grow      oiand-ceii.    Membrana   oo  drops. 
to  be  conspicuous  bodies,  the  colostnnn  cor-  propria. 

,        -T^.  \        T->      1  11        /  -i    ^         Fig-  3'°- — From  .k  Section  of  the 

fiiiscles  (riST-    ^12).      Basket-cells    (remark^,  mammary  Glan-d  of  a  nursing 

^.        \  ,    ,.  .  WOM.AN.     X   230.    Technic  No. 

p.  86)  and  a  delicate  membrana  propria  sepa-  174- 

rate  the  end-pieces  from  the  interstitial  con- 
nective tissue,  that  is   not   only  rich  in  uninuclear  leucocytes,  but  also 
contains  many  oxyphile  cells  (p.  138). 

After  parturition  the  gland-cells  are  larger,  filled  with  stainable 
granules  (precursors  of  the  secretion  ?)  and  with  fat  drops,  which  latter 
usually  lie  on  the  side  of  the  cell  directed  toward  the  gland-lumen  and 
often  exceed  in  size  the  nucleus  of  the  cell  (Fig.  310). 

When  lactation  has  been  established  for  a  couple  of  days  some  of 
the  gland-cells  appear  flat  (empt}^  of  secretion),  some  as  tall  cj'linders, 
that  with  a  ragged  top  extend  toward  the  lumen  ;  both  forms  are  united 
with  each  other  by  transitional  forms  and  contain  (the  tall  cells  more 
often)  two  nuclei.  Both  forms  contain  fat  drops  ;  these  are  not  as  in  the 
sebaceous  glands  the  product  of  a  fatt}'  degeneration  of  the  cell,  but  the 
product  of  an  act  of  secretion,  that  the  cell  repeats  many  times  and  of 
which  it  does  not  perish. f  Besides  the  fat  drops  ("  milk  globules  "),  the 
gland-lumen  contains  free  nuclei,  that  appear  to  be  extruded  from  the 
gland-cells.     These  nuclei  perish  by  liquefying  (t/.  p.  72)  and  regulate  the 

*  Not  seldom  a  stratified  squamous  epithelium,  instead  of  cylinder  epithelium,  is  found  in 
the  trunks  of  the  excretory  ducts. 

t  This  statement  is  not  vitiated  by  the  well-established  fact  that  some  gland-cells  die. 
The  death  of  these  cells  is  due  to  the  intensity  of  their  secretory  activity,  which  may  result  in 
the  rapid  ageing  and  finally  in  the  demise  of  individual  cells. 


394 


HISTOLOGY. 


»^ 


Fig.  311. — From  a  Thick  Section  of  the  Mammary 
Gland  of  a  Woman  Last  Pregnant  Two  Years 
BEFORE.  X  so.  I.  Large  excretory  duct;  2,  small 
excretory  duct;  3,  gland  lobules,  separated  from  one 
another  by  connective  tissue.     Technic  No.  173. 


nuclein  constituent  of  the  milk.*  Colostrum  corpuscles  and  leucocytes 
are  now  wanting,  and  the  greatly  reduced  interstitial  connective  tissue 
contains  extremely  few  leucocytes  and  eosinophile  cells. 

When  lactation  is  ended  a 

*  — -  gradual     regressive      metamor- 

^~~~-~-^  -        phosis  takes  place,  that  is  soon 

"    "^     "  ^  ^-  -         manifested  by  the  abundant  de- 

velopment  of  the  interlobular 
connective  tissue  f  (Fig-  3ii)- 
The  lobules  become  smaller, 
the  end-pieces  begin  to  atrophy. 
In  elderly  persons  all  the  end- 
pieces  and  the  lobules  have  dis- 
appeared and  only  the  excretory 
ducts  remain. 

The  skin  of  the  nipple  and 
of  the  areola  is  characterized  by 
deep  pigmentation,  due  to  the 
presence  of  pigment  granules  in 
the  deepest  strata  of  the  epidermis,  by  tall  papillae,  and  by  the  presence 
of  smooth  muscle-fibers,  which  latter  are  partly  circularly  arranged 
around  the  orifices  of  the  ducts,  partly 
ascend  vertically  to  the  apex  of  the  nip- 
ple. In  the  integument  of  the  areola 
accessory  mammary  glands,  the  areolar 
glands  (Montgomery),  occur  during 
pregnancy  and  lactation. 

The  blood-vessels  approach  the 
mammse  from  all  sides  and  forrn  capil- 
lary networks  embracing  the  gland-tu- 
bules. The  lymph-vessels  form  capillary 
plexuses  lying  within  and  between  the 
gland-lobules.  Lymph-vessel  networks 
also  occur  in  the  vicinity  of  the  am- 
pullae and  the  areolae. 

The  nerves  are  in  part  vascular  nerves,  in  part  behave  like  those  of 
the  glands  of  the  oral  cavity  (p.  247). 


Fig.  312. — A.  Milk  Globules  from  Hu- 
man Milk.  X  560.  Technic  No.  175- 
B.  Elements  of  the  Colostrum  of 
a  Pregnant  Woman.  X  560.  i.  Cell 
containing  uncolored  fat  globules;  2,  cell 
containing  minute  colored  fat  globules; 
3,  leucocyte;  4,  milk  globules.  Technic 
No.  176. 


*  Nuclear  divisions  by  mitosis  do  not  occur  in  the  functionating  mammary  gland ;  it  is 
assumed  that  the  nuclei  here  are  produced  by  amitosis  (remark  *,  p.  69). 

I  Leucocytes  also  reappear,  that  behave  in  exactly  the  same  manner  as  during  the  period 
of  gestation  and  become  colostrum  corpuscles,  etc.  Therefore  the  leucocytes  invariably  are 
present  when  retention  occurs. 


THE    SKIN.  395 

Microscopically  uiilk  consists  of  a  clear  fluid,  the  viilk  plasma^  in 
which  large  fat-drops  from  2  to  5  fj.  in  size,  the  viilk  globules,  are  sus- 
pended. In  addition  isolated  cells  enclosing  fat  globules  (leucocytes)  are 
found  in  milk. 

The  elements  of  milk  secreted  before  and  in  the  first  few  days  after 
parturition  appear  somewhat  different.  Beside  the  milk  globules  the 
colostrum  corpuscles  occxxy,  leucocytes  enclosing  a  spherical  nucleus,  some 
of  which  contain  small,  yellowish  and  larger,  uncolored  fat  globules, 
others  only  uncolored  fat-drops. 

The  ivitchcs'  viilk,  which  can  be  pressed  out  of  the  hollowing  gland- 
ducts  of  the  newborn,  is  a  fluid  resembling  the  colostrum. 


TECHNIC. 

No.  161. — Strata  of  the  skin;  coil-glands. — Cut  from  the  pad  of 
the  finger,  the  palm  of  the  hand,  or  the  sole  of  the  foot  pieces  of  skin, 
as  fresh  as  possible,  from  i  to  2  cm.  square,  together  with  a  thin  stratum 
of  the  subjacent  fat  and  place  them  in  30  c.c.  of  absolute  alcohol.  To 
prevent  curling  of  the  pieces  pin  them  on  small  cork  plates  with  the 
epidermis  turned  toward  the  cork,  and  place  the  whole  in  absolute  alco- 
hol. On  the  following  day  remove  the  pieces  from  the  cork  plates  and 
place  them  for  from  three  to  four  weeks  in  50  c.c.  of  90  per  cent,  alcohol. 
Cut  thin  and  thick  sections.  The  latter  are  indispensable  in  order  to 
obtain  the  excretory  ducts  of  the  coil-glands  in  their  entire  length.  The 
most  suitable  for  this  purpose  is  the  skin  of  children,  from  the  sole  of  the 
foot,  because  the  still  short  ducts  of  the  coil-glands  here  run  vertically 
(Fig.  288).  Stain  with  alum  carmine  for  ten  minutes  (p.  39) ;  the  red 
coils  can  be  seen  with  the  unaided  eye ;  mount  in  xylol-balsam.  Examine 
with  the  low  power.  In  thick  sections  the  papillae  often  are  indistinct, 
because  they  are  encircled  by  the  red-colored  stratum  germinativum  ;  the 
screw-like  ends  of  the  excretory  ducts  are  most  distinctly  seen  when 
the  object  is  faintly  illuminated  or  with  oblique  illumination  (see  p.  55, 
remark  *). 

To  render  the  stratum  granulosum  visible  bulk-staining  with  borax- 
carmine  for  two  or  three  days  (p.  40)  is  recommended.  The  gran- 
ules of  this  stratum  are  then  stained  an  intense  red  (Fig.  290). 

No.  162. — Pretty  preparations  of  the  under  surface  o(  \.\\e  epidermis 
are  obtained  by  fixation  of  shreds  of  the  epidermis  of  the  dorsum  of  the 
foot,  that  often  can  be  detached  from  injected  cadavers,*  in  30  c.c.  of 
absolute  alcohol.  Stain  for  two  minutes  in  Hansen's  hematoxylin  and 
mount  in  xylol-balsam  (Fig.  289). 


*  The  epidermis  can   also  be  detached  from  the  corium   by  macerating  a  little   piece   of 
skin  in  0.33  per  cent,  acetic  acid. 


396  HISTOLOGY. 

No.  163. — For  preparations  of  the  nails  fix  the  distal  finger  joint  of  a 
child  from  eight  to  twelve  years  of  age  (of  adults,  that  of  the  little  finger, 
if  possible  of  women),  two  or  four  weeks  in  100  or  200  c.c.  of  Miiller's 
fluid  (p.  33)  and  harden  in  about  100  c.c.  of  gradually  strengthened  alco- 
hols (p.  35) ;  decalcify  (p.  36) ;  harden  again  and  stain  thick  cross-sections 
ten  minutes  in  alum-carmine  (p.  39);  mount  in  xylol-balsam.  (Fig.  291.) 
In  cutting  sections  place  the  knife  on  the  volar  side  (not  on  the  nail  side) 
of  the  finger  joint.  The  substance  of  the  nail  frequently  shows  differently 
colored  strata.  In  the  nails  of  old  cadavers  the  germ-layer  often 
becomes  loosened  from  the  ridges. 

No.  164. — Elements  of  the  nails. — Place  pieces  of  nail  i  or  2  mm. 
broad,  in  a  test-tube  containing  5  c.c.  of  concentrated  potash-lye  and 
heat  it  over  a  flame  until  it  boils  up  once.  Transfer  the  nail  with  a  drop 
of  the  lye  to  a  slide  and  scrape  off  some  of  the  softened  surface  ;  apply 
a  cover-glass.  On  examination  with  a  high  power  cells  will  be  found 
like  those  in  Fig.  292.  For  comparison  investigate  the  horny  cells  of 
the  stratum  corneum,  which  may  be  obtained  by  lightly  scraping  the 
pad  of  the  finger  with  a  scalpel.  Examine  the  polygonal  scales  in  a 
drop  of  distilled  water,  with  a  high  power. 

No.  165. — Hairs. — Place  a  hair  in  a  drop  of  salt  solution  on  a  slide 
and  examine  it  with  the  low  and  the  high  power  ;  the  most  suitable  for 
study  are  white  hairs  and  the  hairs  of  the  beard.  The  hair  cuticle  of 
man  is  very  delicate  and  the  transverse  markings  produced  by  the  im- 
brication of  the  cells  are  often  very  indistinct ;  usually  only  fine  wavy 
lines  are  visible.  The  hairs  of  many  animals,  on  the  other  hand,  show 
the  cuticula  very  well,  for  example,  sheep's  wool. 

No.  166. — For  the  demonstration  of  the  elements  of  the  hairs,  place 
a  piece  of  hair  i  or  2  cm.  long  in  a  drop  of  pure  sulfuric  acid  on  a  slide 
and  apply  a  cover-glass  ;  press  lightly  on  the  cover-glass  with  a  needle 
and  the  cortical  substance  will  split  into  fibers,  which  consist  of  adherent 
cortical  cells.  Slightly  warm  the  slide,  press  again  with  a  needle,  so 
that  the  cover-glass  becomes  slightly  displaced  ;  numerous  free  elements, 
superficial  scales  and  cortical  cells,  will  then  be  seen  (Fig.  294). 

No.  167. — For  the  exhibition  of  the  elements  of  the  hair  follicles 
(and  the  hairs)  cut  from  a  mustachioed  human  upper  lip  a  piece  2  cm. 
square  and  place  it  in  dilute  acetic  acid  (5  c.c.  of  acetic  acid  to  lOO  c.c. 
of  distilled  water).  In  two  days  the  individual  hairs  with  their  sheaths 
can  be  easily  withdrawn  and  their  elements  separated  by  teasing  in  a 
drop  of  distilled  water  (Fig.  294).  The  cells  of  Henle's  sheath  float  in 
small  complexes  in  the  preparation  and  closely  resemble  fenestrated 
membranes  (Fig.  294,  5).  The  fenestra  are  spaces  normally  occurring 
between  Henle's  cells,  through  which  processes  of  the  cells  of  Huxley's 
stratum  extend  to  the  outer  root-sheath.  Not  infrequently  a  hair-follicle 
is  obtained  in  which  shedding  is  taking  place  (similar  to  Fig.  306). 

No.  168. — For  the  study  oi  hairs  and  liair follicles  place  pieces  2  or 
3  cm.  square  of  the  quite  fresh  skin  of  the  scalp  in  about  200  c.c.  of  a  3 


THE    SKIN.  397 

per  cent,  solution  of  potassium  bichromate  (p.  2i,  No.  lo  a)  for  from  four 
to  eight  weeks  ;  wash  them  for  from  one  to  three  hours  in  running  water 
and  harden  in  the  dark  in  about  lOO  c.c.  of  gradually  strengthened 
alcohol.  Longitudinal  sections  of  sufficient  thinness,  which  include  the 
entire  length  of  the  follicle,  are  very  difficult  to  cut.  Macroscopic  ori- 
entation as  to  the  direction  of  the  hair  is  first  necessary.  To  obtain 
preparations  like  that  in  Fig.  293  thick  unstained  sections  are  to  be 
mounted  in  glycerol.  Thin  sections  usually  include  only  a  portion  of 
the  hair-follicle.  It  is  much  easier  to  cut  thin  cross-sections,  but  care 
must  be  taken  to  make  the  cut  vertical  to  the  longitudinal  direction  of  the 
hair,  not  parallel  to  the  surface  of  the  skin.  In  this  way  hairs  and  hair- 
follicles  at  different  levels  are  obtained  in  a  single  section.  These 
sections  are  to  be  stained  with  Hansen's  hematoxylin  and  with  eosin  * 
(p.  39)  and  mounted  in  xylol-balsam.  Especially  fine  are  the  sections 
of  the  hair-follicles  near  to  the  hair-bulb  (Fig.  295). 

No.  169. — For  the  development  of  hair  cnt  pieces  about  2  cm.  square 
of  the  slcin  of  the  forehead  (not  of  the  hairy  scalp)  of  a  five-  or  six- 
months'-oid  human  embryo  ;  span  them  on  cork  (see  No.  161);  place 
them  for  fourteen  days  in  100  or  200  c.c.  of  Miiller's  fluid(p.  3 3)  and  harden 
in  about  lOO  c.c.  of  gradually  strengthened  alcohols  (p.  35).  Staining  the 
objects  in  bulk  in  borax-carmine  (p.  40)  is  advised  ;  or  the  sections  may 
be  stained  in  Hansen's  hematoxylin  (p.  38).  Embed  the  tissue  in  liver  ; 
endeavor  to  cut  sections  exactly  in  the  direction  of  the  hair-follicle, 
which  is  much  more  easily  done  than  in  the  hairy  scalp  of  the  adult. 
Mount  in  xylol-balsam.  The  sections  exhibit  all  stages  of  development. 
The  preparations  of  figures  302,  303,  and  305  were  fixed  in  Zenker's 
fluid.  The  details  pictured  in  figures  297  to  306  can  be  seen  only  in 
thin  microtome  sections. 

No.  170. — Shedding  and  renewal  of  hair. — The  eyelids  of  newborn 
children  are  most  suitable.  Treat  like  No.  191.  Cut  sagittal  sections. 
Vertical  sections  of  the  hairy  scalp  often  yield  good  results. 

No.  171. —  The  sebaceous  glands. — Fix  and  harden  the  alae  nasi  of 
newborn  children  in  100  c.c.  of  a  3  per  cent,  solution  of  potassium 
bichromate  (like  No.  168).  Cut  thick  (Fig.  307  A)  and  thin  (Fig.  307  B) 
sections  ;  stain  them  with  dilute  carmine  (p.  39),  and  with  Hansen's 
hematoxylin  (p.  38),  and  mount  in  xylol-balsam.  Sections  lengthwise 
of  the  nose  often  show  sebaceous  glands  and  hair-follicles,  but  they 
must  be  exactly  vertical.  The  alae  of  the  nose  of  adults,  on  ac- 
count of  the  v^ery  large  sebaceous  glands  with  their  wide  excretory 
ducts,  do  not  furnish  good  microscopic  specimens.  Small  sebaceous 
glands  with  hair-follicles  can  be  seen  with  the  unaided  eye  in  stripping 
off  the  macerated  epidermis  of  old  cadavers. 

No.  172. —  The  blood-vessels  of  the  skin. — Inject  with  Berlin  blue  the 
entire  hand  of  a  child  through  the  ulnar  artery  or  a  foot  through  the  pos- 

*  Slow  staining  with  eosin  (3  a,  p.  39)  stains  the  granules  of  keratohyaline  an  intense  red 
(Fig.  296). 


398  HISTOLOGY. 

terior  tibial  artery  (p.  48)  and  place  it  in  from  i  to  2  liters  of  Miiller's  fluid 
(p.  33) ;  after  several  days  cut  pieces  2  or  3  cm.  square  of  the  palm  of  the 
hand  or  of  the  sole  of  the  foot,  place  them  for  from  two  to  four  weeks  in 
100  or  200  c.c.  of  Miiller's  fluid  and  harden  them  in  100  c.c.  of  gradually 
strengthened  alcohols  (p.  35).  Cut  thick  sections  and  mount  them  un- 
stained in  xylol-balsam  (Fig.  308).  The  papillae  in  such  sections  often 
can  only  be  recognized  by  the  capillary  loops.  To  the  beginner  it  appears 
as  if  the  loops  extend  into  the  stratum  germinativum. 

No.  173. — For  a  general  view  of  the  mammary  gland  place  the 
nipple  and  a  portion  of  the  gland  (3  or  4  cm.  square)  in  from  60  to  100 
c.c.  of  absolute  alcohol.  If  possible  obtain  the  glands  of  an  individual 
that  was  pregnant  not  too  long  a  time  before,  also  the  glands  of  virgins, 
etc.  Make  vertical  sections  through  the  nipple  and  in  any  direction 
through  the  gland-substance,  and  stain  them  with  Hansen's  hema- 
toxylin (p.  38);  mount  in  xylol-balsam.      (Fig.  311.) 

No.  174. — For  the  minute  structure  of  the  mammary  glands  place 
the  warm,  living  tissue.  (3  to  5  mm.  cubes)  of  a  mammal  during  gesta- 
tion or  lactation  in  5  c.c.  of  Flemming's  mixture  (p.  34),  and  harden 
after  one  or  two  days  in  30  c.c.  of  gradually  strengthened  alcohols.  Cut 
vety  thin  sections,  stain  them  with  safranin  (p.  41),  and  mount  in  xylol- 
balsam.  The  structure  is  often  difficult  to  understand  on  account  of  the 
small  size  of  the  gland-cells  (in  the  rabbit).      (Fig.  309,  310.) 

No.  175. — The  elements  of  milk. — Put  a  drop  of  salt  solution  on  a 
clean  slide  and  add  to  it  a  drop  of  milk.  The  milk  is  to  be  obtained  by 
placing  the  cover-glass  upon  the  nipple  of  a  nursing  woman  and  then 
pressing  out  a  drop.      Examine  with  a  high  power  (Fig.  312  A). 

No.  176. — The  elements  of  colostrum. — Obtain  the  colostrum  from 
a  pregnant  woman  shortly  before  parturition.  Proceed  as  in  No.  175. 
Be  careful  to  avoid  pressure  on  the  cover-glass.  The  nuclei  of  the 
colostrum  corpuscles  can  rarely  be  distinctly  seen  without  further  treat- 
ment ;  on  the  addition  of  a  drop  of  picrocarmine  they  appear  as  simple, 
round,  dull-red  spots  (Fig.  312  B). 


X.    THE   ORGAN   OF  VISION. 

The  organ  of  vision  consists  of  the  eyeball  {bulbus  oculi),  the  optic 
nerve,  the  eyelids,  and  the  lacrimal  apparatus. 

THE    EYEBALL. 

The  eyeball  is  a  hollow  globe,  which  encloses  partly  formed,  partly 
fluid  contents.  The  wall  of  the  globe  is  composed  of  three  membranes  : 
(i)  the  tunica  externa,  a  connective-tissue  membrane,  in  which  an  an- 
terior transparent  division,  the  coriiea,  may  be  distinguished  from  the 
remaining  opaque  portion,  the  sclera  ;  (2)  the  tunica  media,  rich  in  ves- 


THE    ORGAN    OF    VISION.  399 

sels,  which  inckides  three  divisions,  the  choroid,  the  ciliary  body,  and  the 
iris;  (3)  the  tunica  interna,  the /r//;/!^,  which  contains  the  terminal  ap- 
paratus of  the  optic  nerve.  The  formed  contents  within  the  eyeball  are 
the  lens  and  the  vitreous  body. 

The  first  anlage  of  the  eyeball,  \\\t  primary  optic  vesicle,  is  a  hollow  epi- 
thelial sphere,  which  is  connected  with  the  brain  by  a  stalk.  By  invagination 
in  front  and  below  the  primary  vesicle  is  converted  into  the  secondary  vesicle, 
a  two-layered  cup  that  becomes  the  retina  (the  outer  layer  develops  into  the 
pigmented  epithelium  (p.  412),  the  inner  layer  into  the  retina  proper  J  ;  while 
the  stalk  is  transformed  into  the  optic  nerve.  From  the  border  of  the  invagi- 
nation, where  the  inner  and  outer  layers  of  the  secondary  vesicle  meet  and 
blend,  smooth  muscle  fibers  develop,  the  sphincter  and  beside  it  the  dilatator 
pupillte  muscles.*  While  the  vitreous  body  and  the  lens  come  to  lie  within 
the  cavity  of  the  optic  cup,  the  connective  tissue  surrounding  the  cup  separates 
into  two  layers,  an  outer,  which  furnishes  the  tunica  externa,  and  an  inner, 
which  furnishes  the  tunica  media  of  the  eyeball. 

The  Tunica  Externa. 

The  cornea  consists  of  five  strata,  which  named  from  without  in- 
ward form  the  following  (Fig.  313)  :  (i)  the  corneal  epithelium,  (2)  the 
anterior  basal  membrane,  (3)  the  substance  proper,  (4)  the  posterior 
basal  membrane,  (5)  the  corneal  "endothelium." 

The  corneal  cpithclijivi  is  a  stratified  squamous  epithelium  and  con- 
sists of  a  lowermost  layer  of  sharply  contoured  cylindric  cells,  which  is 
followed  by  three  or  four  (more  in  animals)  layers  of  spherical  cells,  that 
in  turn  are  covered  by  several  strata  of  flattened  elements,  still  possess- 
ing nuclei.  The  thickness  of  the  epithelium  in  man  is  0.03  mm.  At 
the  rim  of  the  cornea  the  epithelium  is  continuous  with  that  of  the  con- 
junctival sclera. 

The  anterior  basal  inevibranc  (Bowman's  membrane),  in  man  is  a 
distinctly  visible  stratum,  measuring  up  to  o.oi  mm.  in  thickness,  and 
is  almost  homogeneous  in  appearance.  Its  upper  surface  is  provided  with 
minute  serrations  and  ridges  for  the  attachment  of  the  cylinder  cells  of 
the  corneal  epithelium  ;  at  its  under  surface  it  gradually  passes  into  the 
substantia  propria  of  the  cornea,  of  which  it  passes  as  a  special  modifica- 
tion. The  name  "anterior  elastic  lamina"  is  not  reconmiended,  because 
the  membrane  does  not  consist  of  elastic  substance. 

The  substance  proper  (substantia  propria  corneae)  constitutes  the  chief 
bulk  of  the  cornea.  It  consists  of  delicate  connective-tissue  fibrillae, 
running  a  straight  course,  which  are  united  by  a  (fluid  ?)  interfibrillar 
cement-substance  into  bundles  of  nearly  uniform  thickness  ;  the  bundles 

*  According  to  this  the  muscles  are  of  ectodermal  derivation,  contrary  to  the  majority  of 
other  smooth  muscles,  that  originate  from  the  mesoderm. 


400 


HISTOLOGY. 


in  turn  are  united  by  an  interfascicular  cement-substance  into  flat  lamellae, 
which  lie  in  many  superposed  strata  and  are  held  together  by  an  inter- 
lamellar  cement-substance.  The  lamellae  are  arranged  parallel  to  the 
surface  of  the  cornea  and  run  in  the  direction  of  every  meridian.  A 
number  of  bundles  running  obliquely,  the  so-called  arcuate  fibers,  unite 
each  lamella  with  its  neighbor  above  or  below  ;  especially  well-developed 
arcuate  fibers  occur  in  the  anterior  strata  of  the  substantia  propria. 

Buried  in  the  cement-substance  is  a  system  of  freely  branched 
canals,  the  corneal  canaliculi,  juice  canaliculi,  which  at  many  places  are 
expanded  to   broad,  oval  lacunae,  the  corneal  spaces,  juice-spaces  (Fig. 


Epithelium. 

Anterior  basal  mem- 
brane. 


^^ 


Substantia  propria.    . 


Posterior  basal  mem- 
brane. 


Endothelium.     ^  '\'";v^^-w.^.^v-, 'V^ 

Fig.  313. — Vertical  Section  or  a  Human  Cornea.     X  100.    Technic  Xo.  177  h. 

314).  The  latter  lie  between  the  lamellae,  while  the  canaliculi  also 
penetrate  between  the  bundles.  In  some  animals,  e.  g.  the  frog,  the 
canals  branch  at  right  angles.  The  lacunae  and  canaliculi  contain  a 
serous  fluid  and  cells,  "  fixed  "  corneal  cells  and  wandering  cells  (leuco- 
cytes). The  corneal  cells  are  stellate,  flattened  connective-substance 
cells,  possessing  large,  very  irregularly  shaped  nuclei  (Fig.  315)- 
According  to  one  view  these  cells  lie  against  one  wall  of  the  canal 
system,  according  to  another  opinion  they  completely  fill  the  spaces 
and  canals. 


THE    ORGAN    OF    VISION. 


401 


The  posterior  basal  viC7>ibranc  (membrane  of  Descemet,  posterior 
elastic  lamina)  is  a  transparent  elastic  layer,  only  0.006  mm.  thick.  In 
adult  man  the  posterior  surface,  at  the  periphery  of  the  cornea,  is  beset 
with  hemispherical  elevations,  the  so-called  warts. 

The  corneal  cndotheliinn  is  composed  of  a  single  layer  of  flat,  polyg- 
onal cells  with  spherical  nuclei  (in  animals  the  nuclei  have  the  shape  of 
a  kidney  or  a  horse-shoe).* 

The  sclera  consists  chiefly  of  connective-tissue  bundles,  which  inter- 
lace in  different  directions,  principally  meridional  and  equatorial,  and  of 
many  elastic  fibers f  running  parallel  with  the  bundles,  as  well  as  of  flat, 
connective-substance  cells,  which  like  the  fixed  corneal  cells  lie  in  juice- 


Comeal  canaliculi. 


Corneal  spaces. 


Fig.  314. — Horizontal  Sectign  of  the  Cornea  of 
AN  Ox.  Silver-preparation;  negative  picture; 
the  canalicular  system  is  light  upon  a  dark  ground. 
X  about  240.     Technic  No.  182. 


Fig.  315. — Horizontal  Section  of  the  Cornea  of 
A  Rabbit.  Positive  picture  of  the  corneal  canal- 
iculi.    X  about  240.     Technic  No.  184. 


spaces,  that  are  more  irregularly  shaped  in  the  sclera  than  those  in  the 
cornea.  The  thickness  of  the  sclera  is  greater  at  the  back  (i  mm.)  and 
gradually  diminishes  toward  the  front. 

Between  the  sclera  and  the  choroid  is  a  layer  of  loose  tissue,  rich  in 
elastic  fibers  and  branched  pigment-cells  and  flattened  elements  free 
from  pigment  ("endothelial"  cells),  which  on  separating  the  sclera 
from  the  choroid  adheres  partly  to  the  former  and  partly  to  the  latter  ; 
the  portion  on  the  sclera  is  called  the  lamina  fiisca  scleras,  that  on  the 
choroid,  lamina  siiprachorioidea. 


*  These  forms  are  conditioned  by  the  centrosome  surrounded  by  a  large  court  and  fur- 
ther especially  distinguished  by  the  possession  of  net-like  cords  (^cf.  p.  65). 

t  They  are  especially  profuse  at  the  points  of  insertion  of  the  eye-muscles. 
26 


402 


HISTOLOGY. 


The  Tunica  Media. 
The  choroid  (chorioidea)  is  distinguished  by  the  great  abundance  of 
its  blood-vessels,  which  are  arranged  in  two  layers.  The  superficial 
layer,  lying  to  the  inner  side  of  the  lamina  suprachorioidea,  the  lamina 
vasaUosa  {layer  of  larger  vessels)  (Fig.  316)  contains  the  ramifications  01 
the  arterial  and  venous  vessels,  that  are  enveloped  in  lymph  sheaths  and 
embedded  in  a  ground-substance  (stroma)  consisting  of  delicate  elastic 
fiber-nets  and  numerous  branched  pigment-cells.  In  addition  the  stroma 
contains  the  elements  accompanying  the  larger  arteries  ;  namely,  fibrillar 
connective  tissue,   smooth  muscle-fibers,   and  flat,   nonpigmented    cells, 


3^     ^ 


.Cross  and  longitudinal  sec- 
tions of  bundles  of  sclera] 
fibers. 

Lamina  suprachorioidea. 


Lamina  vasculosa. 


Boundary  zone. 

^^- —  Choriocapillaris. 
^       Basal  membrane. 

Pigment  layer  of  the  retina. 


Fig.  316. — Vertical  Section  through  a  part  of  the  Human  Sclera  and  the  entire  Choroid. 
g.  Larger  vessels;  p,  pigment  cells;  c,  cross-sections  of  capillaries.     Technic  No.  177  c. 


X  100. 


that  are  united  in  delicate  "endothelial"  membranes.  The  deeper 
layer,  the  lamina  choriocapillaris,  or  layer  of  capillary  networks,  is  com- 
posed of  a  narrow-meshed  net  of  wide  capillaries,  between  which  no 
formed  elements  are  found.  Between  the  two  vascular  laminae  lies  the 
boundary  zone  of  the  groimd-siibstance ,  consisting  of  fine  networks  of 
elastic  fibers  and  almost  devoid  of  pigment.  In  ruminants  and  horses 
this  zone  consists  of  wavy  bundles  of  connective  tissue,  to  which  is  due 
the  metallic  reflex  seen  in  the  eyes  of  these  animals.  This  shining 
membrane  is  known  as  the  tapetum  fibrosnm.  The  similar  iridescent 
tapetum  cellulosiim  of  carnivora  is  composed  of  several  strata  of  plate- 
like cells  containing  numerous  minute  crystals. 

Attached  to  the  lamina  choriocapillaris  is  a  close  net  of  fine  elastic 


THE    ORGAN    OF    VISION. 


403 


fibers  and  then  follows  the  lamina  basalis  or  vitreous  membrane,  a  struc- 
tureless lamella,  up  to  2  11  thick,  which  on  its  outer  surface  is  provided 
with  delicate,  lattice-like  markings.      The  polygonal  areas  noticeable  on 


Fig.  317. — A.  From  a  Teased  Preparation  of  a  Human  Choroid.  X  240.  p.  Pigment  cells;  e,  elastic 
fibers ;  A,  nucleus  of  a  flat  nonpigmented  cell ;  the  cell-body  is  invisible. 

B.  Portion  of  a  Human  Choriocapillaris  and  the  adherent  Lamina  basalis.  X  240.  c.  Wide  capil- 
laries, some  of  which  contain  (i)  blood  corpuscles;  e,  lamina  basalis,  showing  a  fine  "lattice- work."  Technic 
No.  178  a. 


its  inner  surface  are  imprints  of  the  retinal  pigment.    The  vitreous  mem- 
brane is  related  to  the  elastic  membranes. 

The  ciliary  body  is  formed  by  the  ciliary  processes  and  the  muscular 
ring  lying  upon  them,  the  ciliary  muscle.     The  ciliary  processes  are  from 


M-. 


-?Sii!i*g^{g; 


Fig.  3i8.^Meridional  Section  through  the  Iridal  Angle  of  Man.  X  30.  i.  Epithelium,  2,  connec- 
tive tissue  of  the  conjunctiva.  3,  Sclera.  4,  5,  6,  7,  and  8.  Ciliary  body;  4,  meridional,  5,  radial,  6,  circu- 
lar fibers  of  the  ciliary  muscle;  7,  ciliary  process;  8,  ciliary  portion  of  the  retina.  9.  Iridal  portion  of  the 
retina.  10.  Stroma  of  the  iris,  xi,  12,  and  13.  Cornea;  11,  posterior  elastic  lamina;  12,  substantia  propria ; 
13,  epithelium.     14.  Venous  sinus  of  the  sclera,     is-  Angle  of  iris.     Technic  No.  177  a. 

seventy  to  eighty  meridionally  placed  folds,  which  begin  low  at  the  ora 
serrata  (p.  414),  gradually  attain  a  height  of  one  millimeter,  and  termi- 
nate with  an  abrupt  descent  near  the  edge  of  the  lens.  Each  ciliary 
process  consists  of  fibrillar  connective  tissue,  that  contains  elastic  fibers 


404 


HISTOLOGY. 


and  numerous  blood-vessels  and  inwards  is  bounded  by  a  continuation 
of  the  vitreous  membrane,  that  here  is  distinguished  by  minute  inter- 
secting folds.  The  blood-vessels  of  the  ciliary  processes  supply  the 
intraocular  fluid. ^"  The  ciliary  muscle  is  an  annular  band  about  3  mm. 
broad,  anteriorly  0.8  mm.  thick,  arising  from  the  inner  wall  of  the  venous 
sinus  of  the  sclera.  The  nonstriped  elements  of  which  it  is  composed 
extend  in  three  different  directions.  We  distinguish  i,  meridional  fibers 
(Fig.  318,  4),  numerous  muscle-bundles,  intermingled  with  elastic  fibers, 
lying  next  to  the  sclera,  which  extend  to  the  smooth  portion  of  the 
choroid;  they  are  known  as  the  tensor  chorioidecB ;  2,  radial  fibers, 
lying  next  to  the  meridional  bundles,  which  from  without  inward  pro- 
gressively assume  a  more  radial  disposition  (oriented  to  the  center  of  the 
bulbus    oculi)  and  posteriorly,   still  in  the  region  of  the  ciliary  body. 


I.  Endothelial  nuclei. 


2.  Anterior  boiindary 
laver. 


3.  Vascular  laj'er. 


4.  Posterior  boundary 
layer. 


S.  Pigment  layer. 


Fig.  319. — Vertical  Section  of  the  Pupillary  Portion  of  a  Human  Iris.  X  loo.  About  one-fifth  of  the 
entire  width  of  the  iris  is  shown,  g.  Blood-vessel,  with  thick  connective-tissue  sheath;  ot,  sphincter  pupiUae 
muscle  cut  transversely;  ^,  pupillary  border  of  the  iris.     Technic  No.  178  c. 


turn  and  follow  a  circular  course  (5) ;  3,  circular  {equatorial^  fibers,  the 
so-called  ring-muscle  of  Midler  (6). 

The  iris  (rainbow  membrane)  consists  of  a  stroma  divided  in  two 
layers,  covered  anteriorly  by  a  continuation  of  the  endothelium  of  the 
cornea  and  posteriorly  by  a  modified  extension  of  the  retina.  Five  layers 
are  distinguished  in  the  iris:  (i)  the  "endothelium,"  (2)  the  anterior 
boundary  layer,  (3)  the  vascular  layer,  (4)  the  posterior  boundary  layer, 
(5)  the  pigment  layer. 

The  endothelium  covers  the  anterior  surface  of  the  iris  and,  like  that 
of  the  cornea,  consists  of  a  single  layer  of  flattened,  polygonal  cells. 

*  The  ciliary  processes  perhaps  serve  to  regulate  the  intraocular  pressure,  that  despite 
the  action  of  the  ciliary  muscle  is  not  increased ;  the  regulation  is  effected  by  compression  of 
the  ciliary  processes. 


THE    ORGAN    OF    VISION.  4O5 

The  anterior  boiuidary  layer  (reticular  layer)  comprises  three  or  four 
strata  of  networks,  which  are  formed  by  stellate  connective-substance 
cells.  This  network  resembles  the  reticulum  of  adenoid  tissue  and  on 
its  posterior  surface  gradually  passes  into  the  vascular  layer. 

The  vascular  layer  of  the  iris  contains  numerous  vessels  radially 
disposed  (to  the  pupil),  in  a  stroma  consisting  of  slender,  loosely  united 
bundles  of  connective  tissue.  There  are  smooth  muscle-fibers  in  the 
vascular  layer,  arranged  in  {a)  circular  fiber-bundles  at  the  pupillary 
margin  of  the  iris,  the  sphincter  pupillce  muscle,  up  to  i  mm.  broad,  and 
(b)  in  animals  (the  rabbit)  a  few  fibers  spreading  in  a  radial  direction 
from  this,  which  do  not  form  a  continuous  stratum  and  are  lost  periphery- 
ward  between  the  fibers  of  the  dilatator  muscle  ;  in  man  only  traces  of 
these  fibers  are  present.  In  the  anterior  boundary  layer  and  in  the  vas- 
cular layer  pigmented  cells  occur  in  greatly  varying  numbers  ;  in  blue 
eyes  they  are  absent. 

The  dilatator  muscle  of  the  pupil  extends  from  the  ciliary  margin  of 
the  iris  to  near  the  pupillary  margin  and  unites  with  the  connective  tissue 
occurring  here  between  the  sphincter  bundles,  there  between  the  bundles 
of  the  ciliary  muscle.  It  consists  of  a  continuous  stratum  of  spindle- 
shaped  smooth  muscle-fibers,  of  which  each  exhibits  an  anterior,  non- 
nucleated,  contractile  division  and  a  posterior,  nucleated,  pigmented 
division  ;  the  anterior  division  in  particular  can  be  distinctly  seen  in 
radial  sections  of  the  iris  and  has  long  been  known  under  the  name  of: 

The  posterior  boundary  layer  (Bruch).  The  posterior  pigmented 
portion  forms  with  the  adjacent,  likewise  pigmented,  polygonal  cells  of 
the  "  pars  iridica  retinae  "  a  common  pigment-mass  : 

The  pigment  layer  of  the  iris.  The  pigment  is  wanting  here  only 
in  albinos.  The  posterior  surface  of  the  pigment  layer  is  covered  by  a 
very  delicate,  little  membrane,  the  limitans  iridis,  a  continuation  of  the 
vitreous  membrane  of  the  pars  ciliaris  retinae  (p.  414). 

The  angle  of  the  iris  (corneal  furrow).  The  place  where  the  tran- 
sition of  the  sclera  into  the  cornea  occurs  is  of  especial  interest,  because 
there  the  iris,  the  cornea,  and  the  ciliary  body  meet.  The  transition  of 
the  sclera  into  the  cornea  is  absolutely  direct ;  the  more  wavy  bundles 
of  the  sclera  without  interruption  in  continuity  pass  over  into  the  slender 
fibril-bundles  of  the  cornea,  the  system  of  juice  canaliculi  of  the  sclera 
communicates  with  that  of  the  cornea.  The  line  of  transition,  micro- 
scopically not  sharply  defined,  is  oblique,  because  the  transformation  of 
the  sclera  into  the  tissue  of  the  cornea  takes  place  sooner  in  the  poste- 
rior than  in  the  anterior  portion  of  the  tunica  externa.  The  posterior 
stratum  of  the  substantia  propria  corneae  and  the  posterior  basal  mem- 


406  HISTOLOGY. 

brane  meet  at  the  periphery  with  the  ciliary  border  of  the  iris  ;  this  place 
is  called  the  angle  of  the  iris  (Fig.  318,  15).  Here  the  iris  sends  toward 
the  posterior  surface  of  the  posterior  basal  membrane  connective-tissue 
processes,  tJie  iridal  processes,  that  in  animals  (cattle,  horses)  are  power- 
fully developed  and  constitute  the  so-called  ligamentuin  iridis  pectinatiim. 
In  man  these  processes  are  scarcely  developed  at  all.  The  posterior  basal 
membrane  at  its  entire  periphery  splits  into  fibers,  which  blend  with  the 
iridal  processes  ;  these  fibers  receive  reinforcements  from  the  elastic  ten- 
dons and  the  intermuscular  connective-tissue  of  the  ciliary  muscle  and 
accessions  in  a  lesser  degree  from  the  sclera.  Accordingly  the  tissues 
that  participate  in  the  construction  of  the  fibers  occupying  the  angle  of 
the  iris  are  contributed  by  all  the  structures  that  meet  one  another  there  : 
the  cornea,  sclera,  iris,  and  ciliary  muscle.  The  endothelium  of  the 
posterior  surface  of  the  posterior  basal  membrane,  continued  on  to  the 
surface  of  the  iris,  forms  a  cover  for  these  fibers.  The  spaces  occurring 
between  these  fibers,  that  stand  in  open  communication  with  the  anterior 
chamber  of  the  eye  and  contain  the  same  fluid,  are  called  the  spaces  of 
Fontana.     In  man  they  are  scarcely  developed. 

The   Tunica  Interna. 

The  transparent  retina,  in  a  perfectly  fresh  condition  colored  red  by 
the  visual  purple,  extends  from  the  entrance  of  the  optic  nerve  to  the 
pupillary  margin  of  the  iris  and  in  this  tract  three  zones  can  be  distin- 
guished :  (i)  \.\\& pars  optica  retince,  the  actual  territorial  expanse  of  the 
optic  nerve  ;  this  portion  of  the  retina,  alone  sensitive  to  light,  clothes 
the  entire  posterior  segment  of  the  eyeball,  to  within  a  short  distance  of 
the  ciliary  body,  where  it  terminates  in  a  sharp,  macroscopically  percep- 
tible, serrated  line,  the  ora  s  err  at  a  ;  (2)  \}i\&  pars  ciliaris  retince ,  extending 
from  the  ora  serrata  to  the  ciliary  margin  of  the  iris  ;  (3)  Wx^  pars  iridica 
retin(B,  which  covers  the  posterior  surface  of  the  iris  from  the  ciliary  to 
the  pupillary  margin.  The  ciliary  and  the  iridal  portion  of  the  retina 
are  together  named  pars  caeca. 

The  pars  optica  retince  falls  into  two  divisions,  an  outer,  the  layer 
of  the  visual  cells  (neuro-epithelial  division),  and  an  inner  layer,  the 
cerebral  division  ;  in  each  of  these  divisions  several  layers  can  be  distin- 
guished, four  in  the  neuro-epithelial,  five  in  the  cerebral ;  if  the  pigment 
layer  (pigment-epithelium)  lying  close  beneath  the  choroid,  that  genet- 
ically belongs  to  the  retina,  is  added,  there  are  ten  layers,  that  counted 
from  without  inward  are  arranged  in  the  order  given  in  figure  320. 

The  elements  of  these  layers  are  only  in  part  nervous  or  epithelial  in 
their  nature  ;  the  other  part  is  formed  of  supporting  snbsta7ice,  that  how- 


THE    ORGAN    OF    VISION. 


407 


ever  is  not  of  the  nature  of  connective  tissue  (see  the  neuroglia  of  the 
spinal  cord,  p.  195).  The  most  conspicuous  elements  of  the  supporting 
tissue  are  the  radial  fibers  (Miiller's  supporting  fibers),  slender  cells,  which 


Capillary. 


—  I.  Pigment     layer  -j 
(not  shown).  i 


— 2.  Layer    of    rods 
and  cones. 


-3.  Membrana  lim- 
itans  externa. 


.  Outer     granule 
layer. 


-5.  Fiber  layer    of    i 

Henle.  ^ 

-6.  Outer  reticular  -, 

layer.  I 


Neuro- 

[-   epithelial 


layer. 


■ — 7.  Inner 
layer. 


granule 


Pyramidal  expansion  of  a  radial-fiber. 


— 8.  Inner    reticular    i     Cerebral 
layer.  [       layer. 


— 9.  GangHon-cell 

layer. 
— 10.  Nerve-fiber 

layer.* 


Fig.  320. — Vertical  Section  of  a  Human  Retina,  from  the  Posterior  Portion  of  the  EyeballI     X  400. 

— (Schaper.) 

extend  from  the  inner  surface  of  the  retina  through  all  the  layers  to  the 
rods  and  cones.     The  inner  end  of 


Pigment  epithelium. 

Rods'and^cones. 

External  limiting  membrane. 

Outer'granule  layer. 

Outer  reticular]|layer. 

Inner  granule  layer. 

Inner  reticular  layer. 

Gangliou-cell  layer. 
Nerve-fiber  layer. 


the  fibers  is  characterized  by  an 
expanded  base,  the  radial-fiber  pyr- 
amid (Fig.  321,  k)  \  the  bases  of 
these  pyramids  are  so  closely  placed 
beside  one  another  that  they  appar- 
ently form  a  continuous  membrane 
on  the  inner  surface  of  the  retina, 
the  so-called  membrana  limitans 
interna  (Fig.  321,  /).  From  the 
apex  of  the  pyramids  the  radial- 
fibers,  with  progressive  decrease  in 
thickness,     proceed     through     the 

inner  reticular  layer  to  the  inner  granule  layer,  where  they  are  pro- 
vided with  a  nucleus  (Fig.  321,  ;/)  ;  from  here  they  pass  through 
the  outer  reticular  and  outer   granule   layers   to   the    external  limiting 

*To  these  the  membrana  limitans  interna  is  added  as  an  eleventh  layer,  but  it  does 
not  represent  an  independent  structure  (see  the  radial  fibers,  p.  407). 


Fig.  321. — Vertical  Section  of  the  Retina  of  a 
Rabbit.  X  240.  k.  Expanded  base  of  radial 
fibers;  «,  nucleated  portion  of  the  same;  /,  "mem- 
brana limitans  interna."     Technic  No.  178  e. 


40  8  HISTOLOGY. 

membrane,  with  which  they  unite.  Throughout  their  entire  course  th^ 
radial  fibers  give  off  lateral  processes  and  lamellae,  especially, profuse 
in  the  outer  granule  layer,  for  the  support  of  the  nervous  elements 
(Fig.  322).  In  addition  to  these  radial  supporting  cells,  concentric  sup- 
porting cells  zx&  found  in  the  outer  reticular  layer  (Fig.  322,  oo)\  they 
extend  parallel  to  the  surface,  are  provided  with  long  processes,  are 
partly  nucleated,  partly  nonnucleated ;  in  the  neighborhood  of  the  en- 
trance of  the  optic  nerve,  in  the  nerve-fiber  layer,  as  well  as  in  the  gang- 
lion nervi  optici,  a  few  glia-cells  are  found.  From  the  surface  of  the 
membrana  limitans  externa  delicate  processes  extend  to  the  rods  and 
cones,  the  bases  of  which  they  embrace  in  crib-like  structures,  the  so- 
called  fiber-baskets  (Fig.  322).  A  portion  of  both  the  reticular  layers 
belongs  to  the  supporting  substance,  as  also  the  small  quantity  of  cement 
substance  in  the  ganglion-cell  layer. 

In  the  more  detailed  description  of  the  individual  layers  of  the 
retina  for  practical  reasons  the  series  will  be  taken  up  in  the  reverse 
order,  from  within  outward. 

THE    CEREBRAL    LAYER. 

The  nerve-fiber  layer  consists  of  naked  axis-cylinders,  which,  ar- 
ranged in  bundles,  are  united  plexus-like.  At  the  entrance  of  the  optic 
nerve,  where  the  layer  is  thickest,  the  fibers  expand  in  a  radial  direction 
to  the  ora  serrata.  The  radial  arrangement  of  the  fibers  is  disturbed  in 
the  territory  of  the  macula  lutea  (p.  412).  The  majority  of  the  axis- 
cylinders  are  centripetal  fibers,  which  originate  from  the  ganglion  cells 
situated  in  the  retina  ;  the  others  are  the  axis-cylinder  processes  of  cerebral 
ganglion  cells,  centrifugal  fibers  (Fig.  322),  which  terminate  in  free  rami- 
fications around  the  large  ganglion  cells  of  the  inner  granule  layer. 

The  ganglion-cell  layer  ("ganglion  nervi  optici")  consists  of  a 
simple  layer  of  large  *  multipolar  ganglion  cells,  containing  Nissl's 
bodies  (p.  1 1  5),  which  send  one  usually  f  unbranched  process  (nerve- 
process)  centralward,  toward  the  nerve-fiber  layer,  one  or  more  branched 
processes  (dendrites)  peripheryward,  toward  the  inner  reticular  layer  ; 
there  the  processes  divide  and  form  delicate  ramifications  spread  out 
parallel  to  the  surface,  in  different  planes,  which  construct  a  dense 
tangle  with  the  processes  of  other  ganglion  cells  (Fig.  322). 

*  A  few  of  these  cells  are  marked  by  their  large  size ;  such  giant  ganglion  cells  occur  at 
tolerably  regular  intervals ;  "twin  ganglion  cells,"  united  with  each  other  by  a  short  bridge, 
have  been  found  in  this  layer;  only  one  of  the  twin  cells  possesses  a  nerve-process. 

f  Recently  collaterals  have  been  found  on  a  few  nerve-processes,  that  turn  back  and 
envelop  neighboring  ganglion  cells  in  their  ramifications  (Fig.  322). 


THE    ORGAN    OF    VISION. 


409 


The  itDier  reticular  /aj'^r  ("  neurospongium,  granular  layer")  con- 
sists of  a  very  delicate  network  of  the  supporting  substance,  which  sup- 
ports a  dense  nervous  tangle  formed  of  the  processes  of  all  the  ganglion 
cells  of  the  retina. 


Fiber-basket. 


Cone  cell. 


Rod  cell. 


Stellate  gan- 
glion cell. 


iJliL. 

101  ■  ■'  oQii-,oa9 

0 


.dljUliAl-,, 


"Radial-fiber  pyramid.^. 


Fig.    322. — Scheme  of  the  Human  Retina.     Supporting  substance  red.      O.  Nucleated  portion  of  radial 
fibers.     Compare  2-10  with  Figure  320. 


Bipolar      ., 

cells.         ^  fl 


Amakrine  ,    ^ 
cells. 


Cenrtifugal 

nerve-fiber. 


Multipolar 

ganglion 

cell. 


The  inner  granule  layer  \nc\\xde.s  elements  named  "granules,"  that 
differ  greatly  in  their  nature.  The  innermost  stratum  consists  of  large 
ganglion  cells,  amakrine  *  cells,  which  send  branched  processes  into  the 

*  That  is,  without  a  long  process  ;  they  were  formerly  called  spongioblasts,  because  they 
were  erroneously  regarded  as  the  producers  of  the  "  neurospongium. " 


41 0  HISTOLOGY. 

inner  reticular  layer.  The  remaining  strata,  for  the  greater  part,  are 
composed  of  small  bipolar  ganglion  cells  ("ganglion  retinae  "),  the  central 
process  of  which  extends  into  the  inner  reticular  layer  and  there  breaks 
up  into  delicate  varicose  branches,  while  the  peripheral  process  passes 
to  the  outer  reticular  layer ;  there  it  divides  fork -like,  spreads  out 
parallel  to  the  surface,  resolves  into  extremely  minute  fibrillse  and 
passes  into  a  subepithelial  tangle  formed  by  felting  with  the  processes 
of  neighboring  ganglion  cells.*  All  bipolar  ganglion  cells  send  up  one 
process  between  the  visual  cells,  that  terminates  near  the  membrana 
limitans  in  a  slightly  thickened  end  (Fig.  322  x).  Finally,  the  nuclei  of 
the  radial-fibers  occur  in  this  layer. 

At  the  border  toward  the  next  outer  layer  lie  small  and  large 
stellate  cells  ;  they  send  many  processes  to  participate  in  the  formation 
of  the  subepithelial  tangle  ;  one  process  runs  toward  the  inner  reticular 
layer,  where  it  terminates  in  delicate  branches,  and  another — the  nerve 
process — after  a  long  horizontal  course  bends  round  in  a  vertical  direc- 
tion and  passes  to  the  nerve-fiber  layer  (this  is  disputed  by  some  authors), 
or  it  breaks  up  in  terminal  ramifications  spread  out  horizontally  (Fig. 
322  -}-),  that  extend  into  the  layer  of  visual  cells. 

The  07iter  7'eticiilar  layer  (subepithelial  layer,  intergranular  layer) 
likewise  is  a  delicate  network  of  supporting  substance,  which  supports 
the  nervous  tangle  just  described.  The  cellular  elements  of  this  layer 
include  the  concentric  supporting  cells  (p.  408)  and  the  "  subepithelial 
ganglion  cells"  (Fig.  322  x) ;  the  latter  are  dislocated  elements  of  the 
ganglion  retinae,  that  differ  from  the  bipolar  ganglion  cells  only  in  their 
compressed  form,  entirely  agreeing  with  the  latter  in  regard  to  their 
terminal  ramifications. 

THE    NEURO-EPITHELIAL    LAYER. 

The  neuro-epithelial  layer  consists  of  two  kinds  of  elements,  the 
rod-visual  cells  and  the  cone-visiial  cells,  that  both  are  distinguished  by 
the  situation  of  their  nucleus  in  the  lower  half  of  the  cell  and  the  sharp 
demarcation  of  the  upper,  nonnucleated  division  from  the  lower  portion 
by  the  perforated  membrana  limitans  externa.  This  gives  rise  to  the 
appearance  of  different  layers  ;  the  inner,  nucleated  portion  of  the  visual 
cells  being  known  as  the  outer  granule  layer,  the  outer  nonnucleated 
division  as  the  layer  of  rods  and  cones.  Between  these  two  lies  the 
limiting  membrane. 

*  Latterly  it  has  been  attempted  to  distinguish  two  forms  of  ganglion  cells,  of  which  the 
one  stands  in  relation  to  the  rod-visual  cells,  the  other  to  the  cone-visual  cells  ;  the  differences 
are  very  insignificant. 


THE    ORGAN    OF    VISION.  4I  I 

The  rod-visual  cells.  The  outer  halves  of  these  elements  are  the 
rods,  slender  cylinders  (60  11  long,  2  //  thick),  which  consist  of  a  homo- 
geneous outer  segment  and  a  finely  granular  inner  segment.  The  outer 
segment  is  the  exclusive  seat  of  the  visual  purple.  The  inner  segment 
possesses  in  its  outer  end  an  ellipsoidal,  fibrillated  body,  X}ci&  fiber-appara- 
tus. The  inner  halves  of  the  rod-visual  cells  are  named  rod-fibers  ;  they 
are  exceedingly  delicate  filaments,  which  are  provided  with  a  nucleated 
expansion,  the  rod-granule.  The  nucleus  is  marked  by  from  one  to 
three  clear,  transverse  bands.  The  basal  end  of  the  cell  terminates  in 
a  minute  process-free,  club-shaped  expansion  (Fig.  322). 

The  cone-visual  cells.  The  outer  halves  of  these  cells,  the  cones, 
likewise  consist  of  an  outer  segment  and  an  inner  segment.  The  outer 
segments  are  conical   and   shorter  than   those  of  the  rods.      The  inner 


21 


^  ^^^  U'  %-k 


Fig.  323. — Isolated  Elements  of  the  Retina  of  ax  Ape.     X  240.     i    Mutilated  ganglion  cell  of  the  ganglion 
of  the  optic  nerve.     2.  Elements  of  the  inner  granule  layer. 

3.  Rod-visual   cells  and  fragments  of  the  same;  below,  two  outer  segments,  one  of  which  exhibits  transverse 

striation,  the  beginning  of  a  disintegration  into  transverse  platelets;  above  are  two  rods,  the  outer  segment 
of  the  lower  one  falling  apart.  Uppermost  are  more  complete  rod-cells;  a,  outer  segment;  i,  inner  seg- 
ment; k,  rod-granule;  x,  fiber-apparatus. 

4.  Cone-visual  cell:  a,  outer  segment;  i,  inner  segment;  k,  cone-granule;  /,  cone-fiber,  torn  at  lower  end;  x,  fiber- 

apparatus. 
5.'  Radial  fiber;  k,  nucleus  of  the  same;  r,  pyramidal  base.     Technic  No.  181. 

segments  are  thick  and  expanded  pouch-like  ;  therefore  the  cone  as  a 
whole  is  flask-shaped.  The  inner  segment  of  the  cones  also  contains  a 
fiber-apparatus.  The  inner  halves  of  the  cone-visual  cells  are  the  cojie- 
fibers ;  these  are  broad  and  rest  with  an  expanded  pyramidal  foot  on 
the  outer  reticular  layer.  The  nucleated  enlargement,  the  cone-granule, 
usually  lies  immediately  to  the  inner  side  of  the  membrana  limitans. 

The  number  of  the  rods  is  much  greater  than  that  of  the  cones. 
The  latter  occur  at  regular  intervals,  so  that  three  or  four  rods  always 
lie  between  two  cones  (Fig.  320). 

The  basal  portions  of  the  visual  cells,  resting  upon  the  outer  reticular 
layer,  usually  are  distinctly  recognized  as  a  special,  radially  striated  layer 
(Fig.  320),  Henle's  fiber-layer ;  in  the  territory  of  the  macula  lutea  (see 
below),  this  fiber-layer  is  particularly  broad  and  gradually  diminishes — 
often  very  unsymmetrically — toward  the  ora  serrata. 


412  HISTOLOGY. 

The  pigmented  epitJielimn  consists  of  a  simple  layer  of  hexagonal 
cells,  which  on  their  outer  surface,  that  directed  toward  the  choroid, 
where  the  nucleus  lies,  are  free  from  pigment  (Fig.  321),  while  their 
inner  division  contains  numerous  rod-shaped,  brown  pigment-granules 
("  fuscin "),  from  i  to  5  //  long.  From  this  inner  division  numerous 
dehcate  processes  extend  between  the  rods  and  cones.  In  albinos  and 
on  the  tapetum  (p.  402)  the  epitheHum  is  free  from  pigment. 

In  the  macula  lutea  and  fovea  centralis,  also  in  the  ora  serrata, 
the  structure  of  the  retina  above  described  presents  noteworthy  modifi- 
cations. 

The  niaaila  liitea  and  fovea  centralis.  In  the  territory  of  the 
macula  the  layers  of  the  retina  exhibit  the  following  variations :  Delicate 
fibers  of  the  optic  nerve  (the  so-called  papillo-macular  bundle)  run 
from  the  optic  entrance  directly  to  the  adjacent  median  portion  of  the 
macula ;  above  and  below  these  fibers  thicker  nerve-fibers  run  from  the 
optic  entrance  convexly  upward  or  downward  and  unite  at  the  lateral 
margin  of  the  macula.  The  ganglion-cell  layer  is  greatly  increased  in 
thickness,  owing  to  the  arrangement  of  the  bipolar  ganglion  cells,  which 
instead  of  a  simple  layer  are  in  many  (up  to  nine)  layers  over  one 
another  ;  also  the  inner  granule  layer,  by  multiplication  of  its  elements,  is 
almost  twice  as  broad.  The  inner  and  outer  reticular  layers  suffer  no 
essential  change.  The  neuro-epithelial  layer  is  composed  of  the  here 
somewhat  smaller  cone-visual  cells  alone.  Already  at  the  margin  of 
the  macula  the  rod-visual  cells  diminish  in  number  and  within  the 
macula  they  are  wanting  altogether  ;  as  a  result  the  cone-fibers  are 
visible  in  a  wide  extent ;  here  they  alone  form  the  fiber-layer  of  Henle. 
The  cone-granules,  on  account  of  their  large  number,  lie  in  several  rows 
one  above  the  other.  The  radial-fibers  no  longer  stand  vertically  to  the 
thickness  of  the  retina,  but  obliquely  toward  the  fovea. 

Toward  the  fovea  centralis,  situated  in  the  middle  of  the  macula, 
the  layers  of  the  retina  become  gradually  thinner  and  are  in  part  totally 
suspended.  With  the  exception  of  a  few  delicate  fibers,  the  nerve-fiber 
layer  first  disappears  ;  then  the  cerebral  layers  blend  with  one  another 
in  a  thin  layer.  In  the  center  of  the  fovea  {^fundus fovecB)  the  neuro-epi- 
thelial layer  (cone-cells)  alone  is  present.  The  decrease  in  the  layers 
differs  individually,  so  that  the  form  of  the  fovea  is  sometimes  flat,  some- 
times deep  with  steep  borders.* 

A  diffuse  yellow  pigment,  soluble  in  alcohol,  saturates  the  macula 
and  the  fovea. 

*The  latter  form  is  shown  by  the  fovea  represented  in  Fig.  324. 


THE    ORGAN    OF    VISION. 


413 


X 


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t**  o—  .-* 

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414  HISTOLOGY. 

In  the  territory  of  the  ora  serrata  a  rapid  diminution  in  the  retinal 
layers  takes  place.  Optic  fibers  and  ganglion  cells  disappear  before 
reaching  the  ora  serrata.  Of  the  visual  cells  the  rod-visual  cells  are  the 
first  to  vanish ;  the  cone- visual  cells  are  still  retained  but  appear  to  be 
deprived  of  their  outer  segment.  Then  the  outer  reticular  layer  is  lost, 
so  that  the  outer  and  inner  granule  layers  become  confluent,  and  finally 
the  inner  reticular  layer  ceases.  The  radial  fibers  of  Miiller,  on  the  con- 
trary, persist  and  are  highly  developed.  [Within  the  region  of  the  ora 
serrata  commonly  smaller  or  larger  clefts  or  even  rather  voluminous 
spaces  occur,  which  are  called  vacuoles  (Fig.  325).  They  are  either 
confined  to  the  neuro-epithelial  layer  or  extend  centrally  into  the  inner 
reticular  layer.  They  are  probably  filled  with  a  lymphatic  fluid.  The 
meaning  of  these  spaces  is  unknown,  but  they  are  certainly  not  to  be 
regarded  as  pathologic  or  senile  changes,  because  they  are  rather  com- 
mon in  the  perfectly  normal  retinae  of  young  individuals. — Editor.] 

The  pars  ciliaris  retincE  consists  of  a  simple  layer  of  slender  cylinder 
cells  (Fig.  325),  which  gradually  originate  in  the  blended  visual-cell  and 
inner  granule  layers.  These  cells  *  send  fibers  from  their  inner  surface, 
that  extend  in  a  horizontal  direction  close  beside  one  another  and  have 
the  appearance  of  a  vitreous  membrane;  farther  front  toward  the  lens 
these  fibers  form  the  zonula  ciliaris  (p.  419).  The  outer  surface  of  these 
cylinder  cells  is  connected  with  pigmented  cells,  a  continuation  of  the 
pigment  epithelium. 

The  pars  uddica  retince,  the  pigment  layer  ot  the  iris,  has  been 
described  [cf.  p.  405). 

With  regard  to  the  connections  of  the  nervous  elements  of  the  retina, 
according  to  the  foregoing  description  the  nerve-processes  of  the  gang- 
lion cells  of  the  ganglion  of  the  optic  nerve,  as  well  as  a  few  stellate  cells 
of  the  inner  granule  layer  (?)  furnish  the  centripetal  optic  fibers,  while 
the  centrifugal  nerve-fibers  terminate  in  free  endings  in  the  inner  granule 
layer.  The  ganglion  cells  of  the  ganglion  retinas  apparently  do  not 
possess  a  nerve-process  ;  their  union  with  the  other  nervous  elements  is 
effected  by  means  of  the  nervous  tangles  in  the  two  reticular  layers, 
and  not  only  as  elsewhere  by  contact  in  the  customary  manner  {cf. 
remarkf,  p.  1 18),  but  also  by  direct  connection  by  means  of  true  anasto- 
moses (not  shown  in  Fig.  322).  The  connection  with  the  visual  cells  is 
effected  by  means  of  the  intraepithelial  processes  of  the  cells  of  the 
ganglion  retinae,  that  terminate  between  (not  within)  the  visual  elements. 


*  According  to  other  representations  these  cells  correspond  to  the  radial  fibers  (p.  407), 
in  which  case  the  fibers  of  the  zonula  (p.  419)  are  supporting  cells  prolonged  to  the  lens. 


-as      >• 

°'^   -Ji 


a  a 


tain      S 
Jg     O 


hJ  / 


'  Vacuole.' 


Radial-fibers  of  Miiiler. 


"S^*:-^' 


i<^ 


Pars'ciliaris  retinae. 


Fig.  325. — Meridional  Section  of  the  Ora  Serrata  and  the  adjacent  portion  of  the  Pars  Ciliaris 
Retin.e  of  a  Man  Thirty-seven  Years  of  Age.     X  180.— {Scliaper.) 


4i6 


HISTOLOGY. 


(Fig.  322,  left,  between  the  second  and  third  rod-fiber.)  Physiologic 
researches  make  it  highly  probable  that  the  visual  cells  constitute  the 
essential  percipient  part  of  the  retina. 

The  Optic  Nerve. 
The  optic  nerve  in  its  entire  intraorbital  course  is  enveloped  in 
sheaths  which  are  processes  of  the  cerebral  membranes.  Outermost  is 
the  dural  sheath,  consisting  of  firm  connective -tissue  bundles,  externally 
having  more  a  longitudinal,  internally  more  a  circular  arrangement,  and 
of  many  elastic  fibers  (Fig.  326)  ;  following  this,  toward  the  interior,  is 
the  very  delicate  arachnoidal  sheath,  which   sends   numerous,  branched 


Central  artery. 
Fibers  of  the  lamina  cribrosa.      |      Central  vein. 


Hyaloid  membrane, 
loosened. 


Bundles  of  optic  nerve 
Pial  sheath 

Arachnoidal  sheath 
Dural  sheath 


Fig.  326. — Longitudinal  Section  of  the  Optic  Entrance  of  a  Human  Eye.  X  15.  Above  the  lamina 
cribrosa  the  narrowing  of  the  optic  nerve  is  visible.  The  central  artery  and  vein  have  been  for  the  most  part 
cut  longitudinally,  but  above  at  several  points  transversely.     Technic  No..  177  d. 


connective -tissue  trabeculae  inward  to  the  pial  sheath,  while  the  union 
with  the  dural  sheath  is  established  by  a  few  tight  fibers.  Innermost 
lies  the  pial  sheath,  which  closely  invests  the  optic  nerve  and  sends  off 
numerous  lamellae,  which  form  sheaths  for  the  individual  nerve-fiber 
bundles.  These  lamellae  are  connected  with  one  another  by  transverse 
trabeculae,  the  resultant  structure  being  a  transverse  lattice-work. 

The  tissue  of  the  pial  sheath  does  not  penetrate  within  the  nerve- 
fiber  bundles,  but  only  forms  an  outer  envelope  for  them.  The  nerve- 
fiber  bundles  con.sist  of  delicate  medullated  fibers  without  a  neurilemma  ; 
they  are  held  together  by  many  long-rayed  neuroglia  cells.  The  same 
are  found  in  greatest    number  on  the  surface  of  the  optic  nerve,  are 


THE    ORGAN    OF    VISION.  417 

numerous  in  the  periphery  of  the  fiber-bundles,  and  their  processes  spin 
themselves  around  each  individual  nerve-fiber.  This  creates  a  con- 
spicuous distinction  between  these  and  the  peripheral  nerves,  in  which 
glia-cells  are  wanting.  At  the  entrance  of  the  optic-nerve  into  the  eye- 
ball the  dural  sheath  passes  into  the  sclera ;  the  arachnoidal  sheath  at  its 
anterior  end  resolves  into  fibers,  so  that  the  subdural  space  lying  on 
its  outer  side  communicates  with  the  subarachnoid  space  on  its  inner 
side.  The  pial  sheath  blends  with  the  sclera,  which  here  is  pierced  with 
numerous  holes  for  the  nerve-fibers  passing  through  it  ;  this  portion  is 
very  rich  in  elastic  fibers  and  is  called  lamina  cribrosa.  The  choroid 
also  participates,  though  in  a  slight  degree,  in  the  formation  of  the  lamina 
cribrosa.  The  nerve-fibers  lose  their  medullary  sheath  at  the  optic 
entrance,  consequently  the  entire  nerve  is  considerably  reduced  in  size, 
and  bending  round  spread  out  radially  on  the  inner  surface  of  the  retina. 
At  the  turning  point  the  fibers  form  a  ring-like  wall  around  the  blood- 
vessels entering  from  the  axis  of  the  optic  nerve  (papilla  nervi  optici), 
that  gradually  levels  towards  the  periphery  (Fig.  326).  The  funnel- 
shaped  depression  encircled  by  the  papilla  varies  greatly  in  size  and  is 
called  the  physiologic  excavation  of  the  optic  nerve. 

The  central  artery  and  central  vein  of  the  retina  lie  in  the  axis  of 
the  distal  half  of  the  optic  nerve  ;  the  connective  tissue  enveloping  these 
vessels  is  freely  connected  with  the  pial  sheath,  as  well  as  with  the  lamina 
cribrosa. 

The  Lens. 

The  more  intricate  structure  of  the  lens  can  be  understood  only  by  con- 
sidering its  developmental  history.  The  lens  arises  by  constriction  from  the 
outer  germ-layer  and  then  represents  a  hollow  vesicle  formed  of  a  simple  layer 
of  cylinder  epithelial  cells.  The  cells  of  the  anterior  wall  of  this  vesicle,  by  a 
trifling  alteration  in  their  form,  become  the  lens  epithelium  ;  the  cells  of  the 
posterior  wall  grow  out  to  long  lens-fibers,  the  number  of  which  undergoes 
considerable  augmentation  by  repeated  division  of  the  cells  situated  at  the 
equator  of  the  lens-vesicle.  Eventually  the  lens-fibers  fill  the  entire  cavity,  so 
that  the  lens  then  represents  a  solid  body,  in  its  chief  bulk  consisting  of  lens- 
fibers — they  are  collectively  designated  the  substantia  lentis — and  only  on  its 
anterior  surface  covered  by  the  lens  epithelium,  which  at  the  equator,  by 
gradual  elongation  of  its  elements,  is  transformed  into  the  lens-fibers.  The 
whole  is  enveloped  in  the  lens  capsule,-  which  perhaps  is  exclusively  developed 
from  the  epithelial  lens-vesicle. 

In  the  substantia  lentis  a  soft  cortical  substance  and  a  firm  core  may 
be  distinguished.  It  consists  entirely  of  epithelial  cells,  greatly  extended 
in  length,  named  the  lejis-fibers.  They  have  the  form  mostly  of  hexag- 
onal, prismatic  bands,  that  at  one  or  both  ends  possess  a  bulbous  enlarge- 
ment. Three  varieties  are  distinguished  :  central  fibers,  transition  fibers, 
27 


4i8 


HISTOLOGY. 


and  chief  fibers.  The  central  fibers  are  nonnuclear,  possess  waved  or  den- 
tated  edges,  and  are  centered  toward  the  axis  of  the  lens.  The  transition 
fibers  have  also  lost  their  nucleus.  These  two  varieties  form  the  core  of 
the  lens.  The  chief  fibers  form  the  major  part  of  the  substantia  lentis 
and  are  distinguished  by  smooth  edges  and  an  oval  nucleus  lying  in  the 
neighborhood  of  the  equator.  All  the  fibers  are  bound  to  one  another 
by  a  small  quantity  of  cement  substance,  that  is  more  abundant  at  the 
anterior  and  posterior  poles  of  the  lens  and  in  maceration  experiments 
leads  to  the  formation  of  the  so-called  anterior  and  posterior  lens- 
stars.  All  lens-fibers  run  in  a  meridional  direction,  beginning  at  the 
anterior  lens-star,  to  the  posterior  lens-star ;  but  no  lens-fiber  embraces 
the  entire  half  of  the  lens  :  the  nearer  the  anterior  pole  a  fiber  arises, 


Fig.  327. — Lens-fibers  of  a  newborn 
L^ANT.  A.  Isolated  lens-fibers,  three 
with  smooth,  one  with  dentated  borders. 
X  240.     Technic  No.  187. 

B.  Human  lens-fibers  cut  transversely;  c, 
section  through  club-shaped  ends. 
X   s6o.    Technic  No.  188. 


(/ 


^  /^r^^fO 


Fig.  328. — Capsule    and    Epithelium  of  a   Lens    of 

ADULT    Man.    C.  Inner   aspect.     X    240.    Technic 

No.  189  a. 
D.  Lateral  aspect,  from  a  meridional  section  _  through  the 

equator  of  the  lens;    i,  capsule;     2,   epithelium;    3, 

lens-fibers.  X  240.  Technic  No.  189  h. 


the  more  remote  from  the  posterior  pole  it  finds  its  terminus.  The 
chief  fibers  are  arranged  in  radial  lamellae,  *  the  number  of  which  in 
adult  man  exceeds  2000. 

The  le7is  epitheli2im  is  composed  of  a  simple  layer  of  cubical  cells, 
low  at  the  anterior  lens-pole  (2.5  /./),  becoming  gradually  higher  toward 


*  In  the  lower  vertebrates  and  in  rodents  among  the  mammals  {e.  g.,  in  the  squirrel)  the 
lamellae  are  of  great  regularity ;  in  apes  and  man,  on  the  other  hand,  very  irregular.  Also  the 
transverse  section  of  the  lens-fibers  in  the  latter  are  marked  by  their  great  irregularity.  In  this 
we  detect  the  expression  of  a  greater  elasticity  and  adaptability  of  the  whole  lens,  that  thereby 
is  peculiarly  fitted  to  respond  to  the  demands  of  accommodation.  It  is  well  known  that  the 
amplitude  of  accommodation  in  man  and  apes  is  very  much  greater  than  in  the  other  mammals. 
Regarding  the  erroneous  account  of  the  construction  of  the  lens  out  of  concentric  lamellae,  see 
Technic  No.  i88. 


THE    ORGAN    OF    VISION.  4I9 

the  equator  ( —  10//),  which  extend  over  the  anterior  surface  of  the  lens 
up  to  the  equator  ;  back  of  the  equator  the  epithelial  cells  are  arranged 
in  meridional  rows,*  which  is  owing  to  the  cell  divisions  and  cell  dis- 
placements that  take  place  at  the  equator.  At  the  posterior  ends  of  these 
rows  the  epithelial  cells  gradually  elongate  and  form  the  lens-fibers. 

The  Iciis  capsule  in  man  is  a  crystal  clear,  elastic  membrane,  from 
6.5  to  25  //.  thick  anteriorly,  from  2  to  7  //  thick  posteriorly. 

The  Vitreous  Body. 

The  ectodermal  vitreous  body,  ectodermal  because  probably  origi- 
nating from  the  anlage  of  the  retina,  consists  of  a  fluid  substance,  the 
vitreous  humor,  and  of  fibers,  which  extend  through  the  fluid  in  all 
directions. f  The  surface  of  the  vitreous  body  is  enveloped  in  a  very 
resistant,  structureless  membrane,  the  hyaloid  vieinbranc,  that  anteriorly 
continues  as  the  vitreous  membrane  of  the  pars  ciliaris  retinae  (p.  414)  and 
in  certain  localities  contains  scanty  fibrils,  as  well  as  a  few  cells.  Of  the 
latter  two  forms  may  be  distinguished  :  (i)  round  cells,  resembling  leuco- 
cytes ;  (2)  stellate  and  fusiform  cells.  Cells  containing  clear  vacuoles 
probably  are  forms  undergoing  degeneration. 

Regarding  the  hyaloid  canal,  see  p.  420. 

The  Zonula  Ciliaris. 
In  a  zone  situated  immediately  anterior  to  the  ora  serrata  delicate, 
homogeneous  fibers  arise  |  from  the  inner  surface  of  the  hyaloid  mem- 
brane, as  well  as  from  the  cells  of  the  pars  ciliaris  retinae,  which  pass 
into  the  depressions  between  the  ciliary  processes  and  toward  the  lens, 
where  they  find  their  attachment,  anteriorly,  posteriorly,  and  at  the 
equator,  on  the  lens  capsule.  These  fibers  in  their  totality  form  a  mem- 
brane, nowhere  of  perfect  continuity,  the  zonula  ciliaris,  the  radial  girdle, 
the  anchoring  structure  of  the  lens.  The  communicating  spaces  occur- 
ring between  the  posterior  zonula  fibers  and  the  anterior  surface  of  the 
vitreous  body  are  named  spatia  zomdaria  (canalis  Petiti).§  The  spatia 
are  not  entirely  closed  toward  the  posterior  chamber  of  the  eye. 

*  In  man  the  rows  are  short  and  not  so  regular  as,  for  example,  in  the  cow  and  the  hog. 

f  A  regular  arrangement  of  the  tissues  of  the  vitreous  body  is  very  difficult  to  demon- 
strate ;  but  recent  pathologic-anatomic  discoveries  give  strong  evidence  that  the  fibers  are 
extended  somewhat  after  the  manner  of  the  septa  of  an  orange. 

\  A  few  zonula  fibers  originating  or  ending  in  the  vitreous  body  support  the  genetic  homo- 
geneity with  the  vitreous  body. 

\  Other  authors  name  the  triangular  space  occurring  between  the  zonula  fibers  going  to 
the  anterior  and  posterior  surfaces  of  the  lens  capsule  the  canal  of  Petit,  which  is  incorrect,  be- 


420  histology. 

The  Blood-vessels  of  the  Eyeball. 
The  blood-vessels  of  the  eyeball  are  separated  in  two  sharply  de- 
fined territories,  which  are  in  communication  only  at  the  entrance  of  the 
optic  nerve. 

I.  Territory  of  the  vasa  centralia  retincB  (Fig.  329). — The  central 
artery  of  the  retina  {ci),  at  a  distance  of  from  1 5  to  20  millimeters  from  the 
eyeball,  enters  the  axis  of  the  optic  nerve  and  runs  within  it  to  the  sur- 
face of  the  optic  entrance.  Here  it  divides  into  two  main  branches,  of 
which  the  one  is  directed  upward,  the  other  downward,  each  of  which, 
subdividing,  supphes  the  entire  pars  optica  retinae  to  the  ora  serrata. 
During  its  course  in  the  optic  nerve  the  artery  gives  off  numerous  small 
branches,  which  enclosed  in  the  processes  of  the  pial  sheath  run  be- 
tween the  nerve-fiber  bundles  and  anastomose  with  small  arteries  {B)  that 
have  entered  the  sheaths  of  the  nerve  from  the  surrounding  adipose  tis- 
sue and  also  with  twigs  of  the  short  ciliary  arteries  (at  c).  In  the  retina 
itself  the  artery  breaks  up  into  capillaries,  which  extend  into  the  outer 
reticular  layer.*  The  veins  proceeding  from  the  capillaries  run  parallel 
with  the  branches  of  the  arteries  and  finally  unite  in  the  vena  centralis 
retincE,  likewise  enclosed  in  the  axis  of  the  optic  nerve  (Fig.  329,  a'^. 

In  the  embryo  a  twig  from  the  central  artery  of  the  retina,  the  hyaloid 
artery,  passes  through  the  vitreous  body  to  the  posterior  surface  of  the 
lens.  The  artery  atrophies  before  birth,  but  the  canal  which  transmitted 
it  may  still  be  found  in  the  vitreous  body  of  the  adult ;  it  is  called  the 
hyaloid  canal,  or  Cloqiief  s  canal. 

II,  Territory  of  the  vasa  cilia^na. — This  territory  is  characterized 
by  the  complementary  veins  taking  a  course  entirely  different  from  that 
of  the  arteries. 

Of  the  arteries,  the  short  ciliary  arteries  (Fig.  329,  Roman  numerals) 
supply  the  smooth  portion  of  the  choroid,  while  the  long  ciliary  arteries 
(Fig.  329,  Arabic  numerals)  and  the  anterior  ciliary  arteries  (Fig.  329, 
Greek  letters)  are  primarily  destined  for  the  ciliary  body  and  the  iris. 

The  branches,  about  twenty,  of  the  sliort  ciliary  arteries  (arteriae 
ciliares  posticae  breves)  penetrate  the  sclera  in  the  vicinity  of  the  optic 
entrance  (I) ;  after  giving  off  twigs  (II)  which  supply  the  posterior  half 

cause  the  zonula  fibers  approaching  the  anterior  and  posterior  surfaces  of  the  lens  form  no 
membranes ;  the  fibers  interlace  in  such  manner  that  one  portion  of  the  fibers  approaching  the 
anterior  surface  of  the  lens  come  from  behind,  while  fibers  proceeding  to  the  posterior  surface 
come  from  in  front. 

*  Only  the  cerebral  layer  of  the  retina  is  vascular ;  in  the  fundus  fovese  centralis  the  cere- 
bral layer  is  absent  and  with  it  the  vessels. 


THE    ORGAN    OF    VISION. 


421 


of  the  surface  of  the  sclera,  the  arteries  break  up  into  a  narrow-meshed 
capillary  network,  the  lamina  choriocapillaris  (III).     At  the  optic  entrance 


Cornea 


S  'l'}'/^     ff    7 


Fig.  329. — Scheme  of  the  Vessels  of  the  Eye,  according  to  Leber.  E.xternal  tunic  stippled,  middle  ttinic 
white,  internal  tunic  and  optic  nerve  stippled  crisscross.     Arteries  light.     Veins  dark. 

Territory  of  the  central  vessels  of  the  retina  (small  Italic  letters):  a,  artery,  a',  vein,  central  of  retina;  6,  anas- 
tomosis with  vessels  of  the  sheath;  c,  anastomosis  with  branches  of  the  posterior  short  cOiary  arteries;  d, 
anastomosis  with  choroidal  vessels. 

Territory  of  the  vessels  of  the  sheath  (large  Italic  letters):  A,  inner,  B,  outer  vessels  of  the  sheath. 

Territory  of  the  posterior  short  ciliary  vessels  (Roman  numerals):  /,  artery,  /',  vein  (short  posterior  ciliary); 
77,  episcleral  arterial,  77',  episcleral  venous  branches  of  the  same;  777,  capillaries  of  the  choriocapillaris. 

Territory  of  the  posterior  long  ciliary  vessels  (Arabic  numerals):  i,  posterior  long  ciliary  artery;  2,  circulus  iridis 
major  cut  transversely;  3,  branches  to  the  ciliary  body;  4,  branches  to  the  iris. 

Territory  of  the  anterior  ciliary  vessels  (Greek  letters):  a,  arter\\  a',  vein  (anterior  ciliary);  3,  connection  with 
the  circulus  iridis  major;  y,  connection  with  the  choriocapillaris;  5,  arterial,  5',  venous  episcleral  branches;  e, 
arterial,  e',  venous  branches  to  the  scleral  conjunctiva;  >;,  arterial,  t)',  venous  branches  to  the  corneal  limbus. 

V,  vena  vorticosa.     5,  cross-section  of  the  venous  sinus  of  the  sclera. 


the  arteries  anastomose  with  branches  of  the  arteria  centralis  retinze  (Fig. 
329,  ^)  and  in  this  way  form  the  cii'cular  artery  of  the  optic  nerve  (circulus 
arteriosus  nervi  optici) ;  at  the  ora  serrata  they  anastomose  with  recurrent 


422  HISTOLOGY. 

twigs  of  the  long  ciliary  and  of  the  anterior  ciliary  arteries  (for  the  latter 
anastomosis  see  Fig.  329,  ^). 

The  two  long  cilia?y  arteries  (dsien^  ciliares  posticae  longae)(i)  like- 
wise penetrate  the  sclera  in  the  neighborhood  of  the  optic  entrance  ;  the 
one  artery  passes  to  the  nasal,  the  other  to  the  temporal  side  of  the  eye- 
ball, between  the  choroid  and  the  sclera  to  the  ciliary  body,  where  each 
artery  divides  in  two  diverging  branches  running  along  the  ciliary  margin 
of  the  iris  ;  by  the  anastomoses  of  these  branches  with  the  branches  of 
the  other  long  ciliary  artery  a  vascular  ring  (2)  is  formed,  the  larger 
arterial  circle  of  the  2m(circulus  iridis  major),  from  which  numerous  twigs 
arise  for  the  ciHary  body  and  ciliary  processes  (3)  and  for  the  iris  (4). 
Near  the  pupillary  margin  of  the  iris  the  arteries  form  an  incomplete  ring, 
the  smaller  arterial  circle  (circulus  iridis  minor). 

The  anterior  ciliary  arteries  (arterias  ciliares  anticse)  come  from  the 
arteries  supplying  the  recti  muscles  of  the  eye,  penetrate  the  sclera  near 
the  corneal  margin,  communicate  with  the  larger  arterial  circle  of  the 
iris  (/'?),  supply  the  ciliary  muscle,  and  send  recurrent  branches  to  unite 
with  the  choriocapillaris  {j).  Before  the  anterior  ciliary  arteries  penetrate 
the  sclera  they  give  off  twigs  toward  the  back  for  the  anterior  half  of 
the  sclera  (5),  toward  the  front  to  the  conjunctival  sclera  if)  and  to  the 
corneal  limbus  (vj).  The  cornea  itself  is  non -vascular,  only  at  the  mar- 
gin, in  the  anterior  lamellse  of  the  substantia  propria,  is  there  a  circum- 
ferential network  of  capillary  loops. 

All  the  veins  run  toward  the  equator,  where  they  converge  to  four 
(more  rarely  five  or  six)  small  stems,  the  whorl  veins  or  vencB  vorticoscB, 
which  forthwith  pierce  the  sclera  (Fig.  329)  and  empty  into  one  of  the 
ophthalmic  veins.  In  addition  there  are  small  complemental  veins 
that  run  parallel  with  the  short  ciliary  arteries  and  the  anterior  ciliary 
arteries,  the  short  ciliary  veins  (Fig.  329,  /')  and  the  anterior  ciliary 
veins  («') ;  the  latter  receive  twigs  from  the  ciliary  muscle,  from  the 
episcleral  vascular  network  (Fig.  329,  ^'),  from  the  conjunctival  sclera 
(e'),  and  from  the  circumferential  capillary  loops  of  the  cornea  (>?').  The 
episcleral  veins  also  communicate  with  the  vense  vorticosae,  at  the  equator 
(at  V).  Finally  the  anterior  ciliary  veins  communicate  with  the  sinus 
venosus  sclerce  (Schlemm)  (5).  This  is  a  venous  wreath  encircling  the 
cornea,  that,  lying  within  the  sclera,  still  possesses  completely  closed 
walls.*  It  takes  up  small  veins  from  the  capillary  network  of  the  ciliary 
muscle. 

*  The  communication  with  the  anterior  chamber  of  the  eye  formerly  described  is  facti- 
tious; the  assertion  that  such  communication  existed  was  based  on  the  fact  that  colored  fluids 
injected  into  the  anterior  chamber  pass  over  into  the  venous  wreath  by  filtration. 


the  organ  of  vision.  423 

The  Lymph  Paths  of  the  Eyeball. 
The  eye  possesses  no  proper  lymph-vessels,  but  a  series  of  inter- 
communicating lymph  spaces.     Two  complexes  of  such  spaces  can  be 
distinguished  in  the  eye,  occupying  an  anterior  and  a  posterior  territory. 
The  anterior  territory  comprises  : — 

1.  The  juice  canaliadi  oi  the  cornea  and  the  sclera. 

2.  The  anterior  chamber  of  the  eye,  which,  by  means  of  the  capil- 
lary cleft  between  the  iris  and  the  lens,  communicates  with — 

3.  The  posterior  chamber  of  the  eye.  The  latter  is  in  open  connec- 
tion with — 

4.  The  spatia  zonularia. 

The  last  three  spaces  stand  in  close  relation  to  one  another  and  may 
be  injected  from  the  anterior  chamber. 
The  posterior  territory  includes  : — 

1.  The  liyaloid  canal  {c2ec^2X\'~,  hyaloideus)  (p.  420);  also 

2.  The  intervaginal  lymph  space,  that  is,  the  subdural  and  the  sub- 
arachnoid space  of  the  sheath  of  the  optic  nerve. 

3.  The  narrow  cleft  between  the  choroid  and  the  sclera  :  the  peri- 
choroidal space. 

4.  The  spatiiim  interfasciale  (Tenon)  which  extends  on  the  dural 
sheath  of  the  optic  nerve,  as  the  supradural  space,  to  the  optic  foramen. 

These  spaces  may  be  injected  from  the  subarachnoid  space  of  the 
brain.  The  content  of  these  spaces  is  a  filtrate  from  the  vessels,  which 
also  saturates  the  vitreous  body.  The  quantity  of  fluid  in  the  perichoroidal 
space,  also  in  the  interfascial  space,  normally  is  exceedingly  minimal. 
Both  these  spaces  serve  to  facilitate  the  movements  of  the  choroid  and 
of  the  eyeball  and  may  be  regarded  as  synovial  spaces. 

The  Nerves  of  the  Eyeball. 
The  nerves  of  the  eyeball  penetrate  the  sclera  in  the  circumference 
of  the  entrance  of  the  optic  nerve  and  run  forward  between  the  sclera 
and  the  choroid;  after  giving  twigs  provided  with  ganglion  cells  to  all 
the  choroidal  vessels,  they  form  upon  the  ciliaiy  body  a  ring  plexus 
intermingled  with  ganglion  cells,  the  ciliary  ganglionic  plexus  (plexus 
gangliosus  ciliaris),  from  which  branches  arise  for  the  ciliary  body,  the 
iris,  and  the  cornea.  The  nerves  of  the  ciliaiy  body  terminate  in  delicate, 
pointed  ends  on  the  blood-vessels  and  on  the  ciliary  muscle,  partly  be- 
tween the  muscle-bundles  of  the  ciliary  body  in  the  form  of  branched 
terminal  trees,  which  perhaps  subserve  the  muscular  sense,  and  partly 
on  the  scleral  surface  of  the  ciliary  body  in  the  form  of  a  delicate  plexus. 


424  HISTOLOGY. 

The  medullated  nerves  of  the  iris  form  networks  and  lose  their  medullary 
sheath  as  they  pass  to  the  pupillary  margin  ;  their  terminal  ramifications 
are  in  part  distributed  to  the  sphincter  and  dilatator  muscles  and  to  the 
vascular  walls,  while  another  portion  forms  a  sensory  plexus  lying 
close  beneath  the  anterior  iridal  surface.  GangHon  cells  are  wanting  in 
the  iris  of  man  and  of  mammals. 

The  nerves  of  iJie  cornea  first  enter  the  sclera  and  form  a  circular 
plexus,  the  plexns  annularis,  surrounding  the  corneal  margin,  from  which 
branches  arise  for  the  conjunctiva  and  for  the  cornea.  In  man  the 
twigs  in  the  conjunctiva  terminate  in  spherical  end-bulbs  (p.  222),  lying 
close  under  the  epithelium  ;  they  are  also  found  in  the  substance  proper 
of  the  cornea,  for  a  distance  of  from  one  to  two  millimeters  within  the 
corneal  limbus.  The  corneal  nerves  lose  their  medullary  sheath  after  en- 
trance in  the  substantia  propria,  and  as  naked  axis-cylinders  penetrate  the 
entire  cornea.      They  form  networks,  which  according  to  the  plane  they 


Epithelium. 
Anterior  basal  membrane 

Portion  of  substantia  propria. 

Fig.  330. — From  a  Vertical  Section  through  the  Human  Cornea.  X  240.  n.  A  di\'iding  nerve  pene- 
trating the  anterior  basal  membrane  ;  s,  subepitheUal  plexus  beneath  the  cylindrical  cells  ;  a,  fibers  of  the 
intraepithelial  ple.xus  ascending  helvjeen  the  epithelial  cells.     Technic  Xo.  186. 

occupy  are  described  as  the  stronia-plexiis,  which  lies  in  the  deeper  strata 
of  the  cornea  ;  the  sub-basal  plexus,  which  is  situated  beneath  the  ante- 
rior basal  membrane  ;  the  subepithelial plexics,  which  lies  close  under  the 
epithelium.  From  the  latter  plexus  exquisitely  delicate  nerve-fibrillae 
ascend  into  the  epithelium  between  its  elements  and  form  the  exceed- 
ingly fine  intraepithelial  plextis,  the  ramifications  of  which  terminate  in 
free  ends  between  the  epithelial  cells.  The  nerves  found  in  the  sclera 
form  a  plexus  on  the  blood-vessels  and  in  the  lymph  spaces,  on  which 
latter  endings  occur  in  the  form  of  thickly  branched  structures.  In 
addition  free  nerve-endings,  like  those  in  the  dura,  are  found. 

The  Eyelids. 

The  eyelids,  palpebrcs,  are  folds  of  the  external  skin,  which  enclose 

muscles,  loose  and  compact  connective  tissue,  and  glands.      The  outer 

leaf  of  the  eyelid  retains  the  usual   character  of  the   external  skin  ;  the 

inner  leaf,  that  toward  the  eyeball,  is  considerably  modified  and  is  called 


THE    ORGAN    OF    VISION. 


425 


the  palpebral  cojijiinctiva.  The  external  skin  of  the  eyelid  extends  over 
the  anterior  free  margin  of  the  lid  and  does  not  pass  into  the  palpebral 
conjunctiva  until  it  reaches  the  posterior  border,  "CciQ  palpebral  border. 

The  construction  of  the  eyelid  is  best  studied  in  sagittal  sections 
(Fig.  331).  Counting  from  before  backward  the  following  strata  are 
found  : 

I.   The  external  skin,  which  is  thin  and  beset  with  fine  lanugo  hairs, 


McR  R"  £71 


Fig.  331. — Sagittal  Section  of  the  Upper  Eyelid  of  a  Child  six  months  old.  X  10.  i.  Integument:  E, 
epidermis;  C,  coriunr;  Sc,  subcutaneous  tissue;  Hb,  hair-follicles  of  lanugo  hairs;  K.  coil-gland;  \V,  eye- 
lash, with  the  anlage  of  a  new  hair  {Eh) ;  W,  W",  portions  of  follicles  of  eyelashes ;  J/,  portion  of  a  ciliary 
gland.  2.  Territory  of  the  orbicularis  palpebrarum  muscle:  O,  bundles  of  this  muscle  cut  transversely;  McR, 
tarsal  muscle.  3.  Expanded  tendon  of  the  levator  palpebrarum  superior;  w/ii,  superior  palpebrarum  muscle. 
4.  Conjunctival  pwrtion:  e.  conjunctival  epithelium;  tp,  tunica  propria;  at,  accessory  tear-gland;  /,  tarsus; 
m,  tarsal  glands,  the  mouth  of  the  e.tcretory  duct  is  not  shown;  a,  transverse  section  of  the  arcus  tarseus; 
a',  transverse  section  of  the  arcus  tarseus  extemus.     5.  Margin  of  the  eyelid.     Technic  No.  191. 

the  follicles  of  which  it  encloses  ;  in  the  corium  small  coil-glands  are 
found,  also  pigmented  connective-substance  cells,  that  as  is  well  known 
are  of  rare  occurrence  in  the  corium  elsewhere.  The  subcutaneous 
tissue  is  very  loose,  rich  in  fine  elastic  fibers,  poor  in  fat-cells,  that  may 
be  entirely  wanting.  Near  the  border  of  the  lid  the  corium  is  more 
compact  and  beset  with  more  conspicuous  papillae.  In  the  anterior  edge 
of  the  margin  of  the  lid  two  or  three  rows  of  robust  hairs,  the  cilia  (W), 


426  HISTOLOGY. 

are  obliquely  implanted,  the  follicles  of  which  extend  far  into  the  corium. 
The  cilia  undergo  rapid  shedding  ;  their  length  of  life  is  said  to  be  about 
from  one  hundred  to  one  hundred  and  fifty  days  ;  consequently  new 
hairs  in  all  stages  of  development  are  frequently  found  among  the  eye- 
lashes {cf.  p.  383).  The  hair-follicles  of  the  cilia  are  provided  with 
small  sebaceous  glands,  in  addition  to  which  they  take  up  the  excre- 
tory ducts  of  the  ciliary  glands  (Moll)  (M)  which  in  their  minute 
structure  resemble  the  coil-glands,  from  which  they  differ  only  in  hav- 
ing their  lower  end  less  convoluted. 

2.  Posterior  to  the  subcutaneous  tissue  lie  the  transverse  bundles  of 
the  cross-striated  muscle-fibers  of  the  orbicularis  palpebrarum  muscle ; 
the  portion  of  the  muscle  lying  behind  the  cilia  (McR)  is  named  the 
tarsal  muscle  (Riolan). 

3.  Behind  the  muscle  the  expansion  of  the  tendon  of  the  levator 
palpebrse  muscle  is  met,  which  is  partly  lost  in  the  connective  tissue 
present,  the  so-called  fascia  palpebralis,  and  partly  attached  to  the  upper 
margin  of  the  tarsus*;  the  latter  portion  contains  smooth  muscle- fibers 
{mps),  the  superior  palpebral  muscle  (Miiller). 

4.  The  tarsus  is  a  plate  of  dense-fibered  connective  tissue,  which 
gives  firmness  and  support  to  the  eyelid.  It  lies  immediately  in  front 
of  the  palpebral  conjunctiva,  to  which  it  belongs,  and  occupies  the  lower 
two-thirds  of  the  height  of  the  entire  eyelid.  In  its  substance  the  tarsal 
glands  (Meibom)  (;«)  are  embedded,  elongated  bodies  which  consist  of  a 
wide  excretory  duct,  opening  on  the  palpebral  border,  and  of  little  vesi- 
cles with  short  stalks,  that  empty  into  it  on  all  sides.  In  their  histology 
the  tarsal  glands  agree  with  the  sebaceous  glands.  At  the  upper  end 
of  the  tarsus,  partly  enclosed  in  its  substance,  lie  branched  tubular 
glands,  which  in  their  minute  structure  coincide  with  the  tear-glands  and 
therefore  are  called  accessory  tear -glands  {¥ig.  331,  at)  ;  they  principally 
occur  in  the  inner  (nasal)  half  of  the  eyelid. 

Behind  the  tarsus  lies  the  conjunctiva  proper,  which  consists  of  an 
epithelium  {e)  and  a  tunica  propria  {tp).  The  former  is  a  stratified  cylin- 
der epithelium,  with  several  strata  of  spherical  cells  in  the  depths  and  a 
stratum  of  mainly  short  cylindrical  cells  on  the  surface.  The  latter 
possess  a  narrow  hyahne  cuticular  border.  Goblet-cells  also  occur  in 
varying  number.  At  the  posterior  palpebral  border  the  epithelium 
gradually  passes  into  the  stratified  squamous  variety,  that  occasionally 
extends  far  over  on  the  palpebral  conjunctiva.     The  lower  portion  of  the 


*  In  the  lower  eyelid  the  expansion  of  the  inferior  rectus  muscle  likewise  contains  smooth 
muscle-fibers,  the  inferior  palpebral  ?miscle. 


THE    ORGAN    OF    VISION.  42/ 

palpebral  conjunctiva  is  smooth.  In  the  upper  portion,  on  the  contrary, 
the  epithelium  forms  irregular  pocket-like  depressions,  the  "  conjunctival 
recesses,"  that  differ  greatly  in  individual  development  and  in  sections, 
when  highly  developed,  may  resemble  glands.  The  tunica  propria  of  the 
conjunctiva  consists  of  connective  tissue,  of  lymphoid  cells  and  plasma- 
cells  in  varying  number.  In  animals,  especially  in  ruminants,  the  latter 
form  true  nodules,  the  so-called  traclwma  glands,  from  the  summit  of 
which  leucocytes  wander  through  the  epithelium  to  the  surface ;  in 
man  the  migration  of  leucocytes  also  occurs  but  in  a  slighter  degree. 
In  the  region  of  the  conjunctival  recesses  the  tunica  propria  is  divided 
into  papillae  by  the  above  described  depressions  of  the  epithelium,  hence 
the  name  "papillary  body." 

The  palpebral  conjunctiva  passes  from  above  (on  the  lower  lid  from 
below)  over  to  the  eyeball,  the  anterior  surface  of  which  it  covers.  At 
the  turning  point,  \\\&  fornix  cojijiinctivce,  a  loose  sub-conjunctival  tissue 
consisting  of  connective-tissue  bundles  occurs  under  the  tunica  propria. 
The  epithelium  is  the  same  as  that  on  the  palpebral  conjunctiva  ;  the  tunica 
propria  contains  fewer  leucocytes,  but  also  in  man  normally  possesses  up 
to  twenty  small  lymph  nodules  and  a  few  mucous  glands.  The  scleral 
conjunctiva  is  modified  in  so  far  that  its  stratified  cylinder  epithelium  within 
a  certain  distance  of  the  cornea  is  transformed  into  the  stratified  squamous 
variety,  which  continues  in  that  of  the  cornea  {cf.  also  Fig.  318). 

The  rudimentary  tldrd  eyelid  (plica  semilunaris)  consists  of  connec- 
tive tissue  and  stratified  squamous  epithelium.  The  caruncula  lacrimalis 
resembles  the  external  skin  in  minute  structure,  only  the  stratum  cor- 
neum  is  absent,  and  contains  fine  hairs,  sebaceous  and  accessory  tear- 
glands. 

The  blood-vessels  of  the  eyelids  proceed  from  branches  approach- 
ing from  the  outer  and  inner  angles  of  the  eye,  that  form  an  arch,  the 
arcus  tarseiis  (Fig.  331,  a),  at  the  margin  of  the  lid,  and  a  second  arch, 
the  arcus  tarseus  extenms  {a'\  at  the  upper  end  of  the  tarsus.  Branches 
from  these  arches  ramify  in  the  skin,  surround  the  tarsal  glands,  and 
penetrate  the  tarsus  to  supply  a  capillary  network  lying  beneath  the  con- 
junctival epithelium  ;  they  also  supply  the  fornix  conjunctivae,  the  scleral 
conjunctiva,  and  anastomose  with  the  anterior  ciliary  arteries. 

The  lymph-vessels  form  a  very  dense  network  in  the  tarsal  conjunc- 
tiva, a  very  thin  network  on  the  anterior  surface  of  the  tarsus.  Accord- 
ing to  some  authors  the  lymph-vessels  of  the  scleral  conjunctiva  are 
closed  at  the  corneal  limbus  ;  according  to  others  they  send  minute 
canaliculi  into  the  tissue  of  the  cornea  and  through  these  are  in  com- 
munication with  the  juice-canal  system. 


428  HISTOLOGY. 

The  nerves  form  a  very  dense  plexus  in  the  tarsus  and  in  the  pal- 
pebral conjunctiva,  which  is  characterized  by  a  peculiar,  coil-like,  twisted 
arrangement  of  its  fibers.  One  portion  of  the  tarsal  plexus  surrounds 
the  tarsal  glands  *  and  here  consists  of  many  nonmedullated  and  few 
medullated  nerve-fibers  ;  another  portion  terminates  in  the  walls  of  the 
blood-vessels.  From  the  "conjunctival  plexus"  medullated  nerve-fibers 
arise,  that  run  obliquely  toward  the  margin  of  the  lid  and  the  palpebral 
conjunctiva,  lose  their  medullary  sheath,  in  part  penetrate  directly  into 
the  epithelium,  where  they  ramify  and  terminate  in  free  endings,  also  in 
end-bulbs  (p.  222)  lying  close  under  the  epithelium.  These  end-bulbs 
are  found  in  large  numbers  not  only  in  the  papillae  of  the  margin  of 
the  lid  and  in  the  palpebral  conjunctiva,  but  also  in  the  ocular  conjunc- 
tiva and  in  the  margin  of  the  cornea  {cf.  p.  424). 

The  Lacrimal  Organ. 
The  lacrimal  gland  IS  a  compound  tubular  gland  provided  with  sev- 
eral excretory  ducts.     The  excretory  ducts  (Fig.   332,^)   are  clothed 


Fig.  332. — From  a  thin  section  of  a  Human  Lacrimal  Gland.  X  240.  A.  Gland-body;  a,  tubule  cut 
transversely ;  a',  group  of  tubules,  mostly  cut  obliquely,  the  lumen  of  only  one  tubule  visible,  below;  s,  inter- 
calated tubule  vrith  cubical  (above  to  the  right)  and  flat  (below  to  the  left),  epithehal  cells;  s",  intercalated 
tubule  in  cross-section,  lined  with  moderately  high  cylindrical  cells;  b,  connective  tissue.  B.  Cross-section 
of  an  e.'ccretory  duct;  e,  two-rowed  cylindrical  epithelium;  b,  connective  tissue.     Technic  No.  192. 

with  a  two-row  cylinder  epithehum  and  gradually  pass  into  long  inter- 
calated divisions,  narrow  tubes  clothed  with  low  epithelium  (Fig.  332 
A,  s  s').  These  finally  continue  in  tubules  that  are  clothed  with  two 
forms  of  cells  and  enveloped  in  a  membrana  propria.  The  gland 
cells  of  the  one  form  in  the  replete  state  are  tall,  but  when  empty  of 
secretion  are  considerably  shorter.  The  secretion  collecting  center  lies 
in  the  lumen  half  of  the  cell.      The  cells  of  the  other  form  are  low  ;  the 

*  Whether  nerve -fibers  penetrate  between  the  gland-cells  has  not  yet  been  distinguished 
with  certainty ;  probably  the  nerves  of  the  tarsal  glands  behave  like  those  of  the  glands  of  the 
mouth  cavity  (p.  247). 


THE    ORGAN    OF    VISION.  429 

secretion  balled  together  in  large  globular  masses  occupies  the  entire 
cell,  except  a  small  zone  at  the  cell-base.  Intercellular  secretory  capil- 
laries, as  well  as  secretion  granules  (the  latter  in  the  cat),  have  been 
demonstrated.  Between  the  gland-cells  and  the  membrana  propria  lie 
a  few  flat  cells,  extensions  of  the  deep  stratum  of  the  epithelium  of  the 
excretory  duct. 

Blood-vessels  and  nerves  behave  as  in  the  glands  of  the  oral  cavity, 
but  the  terminal  ramifications  of  the  latter  are  said  to  form  an  interepi- 
thelial  net. 

The  walls  of  the  lacrimal  canalicidi  consist  of  a  stratified  squamous 
epithelium,  of  a  tunica  propria  rich  in  elastic  fibers,  beneath  the  epithelium 
also  rich  in  cellular  elements,  and  of  cross-striped  muscle-fibers,  for  the 
greater  part  running  longitudinally. 

The  lacrimal  sac  and  the  naso-lacrimal  duct  consist  of  a  two-rowed 
cylinder  epithelium  and  of  a  tunica  propria  which  is  chiefly  adenoid  in 
character  and  separated  from  the  underlying  periosteum  by  a  dense 
plexus  of  veins. 

TECHNIC. 

No.  177. — Carefully  cut  the  fresh  eyeball  out  of  the  optic  cavity 
and  secure  as  much  as  possible  of  the  optic  nerve  ;  then  with  the  scis- 
sors remove  the  attached  fat  and  muscle  and  with  a  sharp  razor  make  an 
incision  at  the  equator,  about  i  cm.  long,  through  all  the  membranes  of 
the  eye.  Then  place  the  eyeball  in  150  c.c.  of  potassium  bichromate 
acetic  acid  solution  (p.  32)  ;  after  from  twelve  to  twenty  hours,  beginning 
at  the  incision  already  made,  divide  the  eyeball  with  the  scissors  com- 
pletely into  an  anterior  and  a  posterior  half  and  change  the  fluid.  After 
another  twelve  or  twenty  hours  wash  the  pieces  and  harden  them  in  100 
c.c.  of  gradually  strengthened  alcohols  (p.  35). 

{a)  Carefully  remove  the  lens  from  the  anterior  half  of  the  eyeball 
and  treat  it  further  like  No.  188  ;  then  cut  out  a  quadrant  and  with  the 
attached  ciliary  body  and  iris  embed  it  in  liver  and  cut  sections  through 
the  iris  angle.  The  thick  sections  are  to  be  stained  with  Hansen's  hema- 
toxylin (p.  38)  and  mounted  in  xylol-balsam  (Fig.  318). 

{b)  From  the  remaining  three-fourths  of  the  anterior  half  of  the 
eyeball  cut  out  a  piece  of  the  cornea,  5  or  lo  mm.  square,  embed  it  in 
liver  and  make  sections  through  the  strata  of  the  cornea  (Fig.  313).  The 
alternating  lamellae  of  the  substantia  propria  can  only  be  well  seen  in 
unstained  sections  mounted  in  dilute  glycerol. 

(c)  From  the  posterior  half  of  the  eyeball  cut  pieces  including  the 
three  tunics,  5  or  10  mm.  square,  and  cut  sections,  not  too  thin,  for  the 
study  of  the  strata  of  the  sclera  and  choroid  (Fig.  316).  Stain  them  with 
Hansen's  hematoxylin  and  mount  in  xylol-balsam.  In  sectioning,  the 
retina  usually  becomes  loosened. 

(d)  For  preparations  showing  the  entrance  of  the  optic  nerve  cut 
around  the  point  of  entrance  at  a  distance  of  about  5  mm.  from  the  same 


430  HISTOLOGY. 

through  all  the  tunics  of  the  eye  ;  embed  this  portion  with  about  one 
centimeter  of  the  optic  nerve  in  hver  and  cut  sections  (not  too  thin). 
Place  the  knife  so  that  it  strikes  the  retina  first,  then  the  choroid  and 
sclera,  and  passes  through  the  optic  nerve  longitudinally  ;  stain  with  dilute 
carmine  (p.  39)  and  with  Hansen's  hematoxylin  (p.  38),  and  mount  in 
xylol-balsam.      Examine  with  very  low  magnification  (Fig.  326). 

No.  178. — Remove  a  fresh  eyeball  according  to  the  method  given 
in  No.  177,  make  an  incision  *  at  the  equator  and  place  it  in  from  100  to 
200  c.c.  of  Miiller's  fluid  (p.  33).  In  from  twelve  to  twenty  hours  divide 
it  with  the  scissors  into  an  anterior  and  a  posterior  half.  In  two  or  three 
weeks  carefully  wash  both  halves  in  slowly  running  water  for  from  one 
to  two  hours.  Then  cut  out  pieces  including  all  the  tunics,  about  8  mm. 
on  a  side,  and  use  for  them  the  following  preparations  : — 

(a)  Teased  preparation  of  the  choroid. — Tease  and  mount  a  frag- 
ment in  a  drop  of  dilute  glycerol ;  it  exhibits  large  blood-vessels, 
capillaries  of  the  choriocapillaris,  branched  pigment-cells,  elastic  fibers, 
sometimes  also  the  lamina  basalis  ;  the  "  lattice-work  "  of  the  latter  is 
often  indistinct.  Isolated  membranes  may  be  stained  with  Hansen's 
hematoxylin  and  mounted  in  xylol-balsam,  but  the  more  deHcate  struc- 
tures are  thus  rendered  indistinct  (Fig.  317). 

(b)  Elements  of  the  retina. — Carefully  tease  a  smallpiece  of  the  retina 
in  a  drop  of  Miiller's  fluid.  Along  with  many  fragments  of  the  elements 
a  few  more  or  less  well-preserved  parts  will  be  found.  Human  eyes  have 
very  large,  beautiful  cone-visual  cells,  while  those  of  many  mammals,are 
very  small ;  wholly  unsuitable  in  this  respect  are  the  eyes  of  the  rabbit ; 
unfortunately,  human  eyes  are  usually  no  longer  in  a  sufficiently  fresh 
condition  when  the  investigation  is  made.  The  outer  segments  of  the 
cones,  also  of  the  rods,  are  extremely  delicate  and  rapidly  disintegrate 
after  death,  falling  into  transverse  plates  and  at  the  same  time  curv- 
ing like  a  shepherd's  crook.  Later  they  disappear  entirely.  In  order 
to  see  beautiful  cone-visual  cells  examine  according  to  the  method 
just  given  the  eyes  of  fishes.     (See  further.  No.  180  and  No.  181.) 

{c)  The  remaining  parts  of  the  eyeball  are  to  be  transferred  from 
the  water  to  80  c.c.  of  gradually  strengthened  alcohols  (p.  35)  for  hard- 
ening ;  when  the  hardening  is  completed  cut  out  the  iris,  embed  it  in 
liver,  and  make  meridional  and  equatorial  sections  ;  stain  them  in  Han- 
sen's hematoxylin  (p.  38)  and  mount  in  xylol-balsam  (Fig.  319). 

{cT)  Cut  out  a  portion  i  cm.  long  of  the  retina,  including  the  ora 
serrata,  which  is  macroscopically  visible  as  a  wavy  line,  embed  it  in  liver, 
and  make  meridional  sections  ;  stain  them  in  hematoxylin  (p.  38)  and 
mount  in  xylol-balsam  (Fig.  325).      The  pictures  are  often  very  intricate. 

(^)  Treat  in  the  same  manner  a  piece  of  the  retina,  which  is  best 
taken  from  the  posterior  portion  of  the  eye,  where  the  optic-fiber  stratum 
is  thickest.  The  radial-fibers  of  Miiller  fcan  be  seen  in  their  entire 
length  only  in  accurate  vertical  sections  (Fig.  320  and  Fig.  321). 

*The  unopened  eyeball  can  be  put  in  the  Miiller's  fluid  for  2  or  3  weeks  and,  after 
washing,  then  divided  and  put  into  the  alcohol. 


THE    ORGAN    OF    VISION.  43  I 

(/)  In  the  same  manner  treat  meridional  sections  through  the 
macula  z.\\di  fovea. '^  It  is  not  difficult  to  cut  sections  of  the  macula,  but 
on  the  other  hand  very  difficult  to  obtain  satisfactory  sections  of  the  ex- 
tremely delicate  fovea.  The  retina  should  not  be  loosened  from  the 
choroid,  but  the  two  should  be  sectioned  together. 

No.  179. — TJie  retina,  after  Golgi. — For  this  purpose  tJiick  retinae 
are  most  suitable,  therefore  select  the  eyes  of  large  animals.  Divide  the 
eye  into  an  anterior  and  a  posterior  half,  remove  the  vitreous  body,  and 
with  forceps  and  scissors  carefully  dissect  a  piece  of  the  retina  from  the 
choroid.  Cautiously  roll  this  piece  into  a  cylindrical  or  spherical  clump 
and  dip  it  for  one  second  in  thin  celloidin  solution  ;  expose  it  for  a  few 
seconds  to  the  air,  until  the  envelope  of  celloidin  is  somewhat  stif- 
fened, and  then  place  the  piece  in  the  Golgi  mixture  (p.  21).  (The  object 
of  this  rolling  in  of  the  retina  is  to  prevent  the  formation  of  precipitates  on 
its  surface.)  Let  the  object  remain  in  the  Golgi  mixture  for  from  twelve 
to  seventy-two  hours,  then  transfer  it  for  twenty-four  hours  to  the  silver 
solution  (p.  46).  Then  repeat  the  procedure  (p.  47).  The  impregnation 
occurs  first,  after  twelve  hours,  in  the  rods  and  cones  ;  after  another 
twelve  hours  in  the  bipolar  cells  and  the  amakrines,  later  in  the  cells  of 
the  ganglion  nervi  optici  and  in  the  nerve-fibers,  last  in  the  supporting 
cells. 

Potassium-bichromate-formol  furnishes  good  results  (p.  33).  Fixa- 
tion of  rods  and  cones,  also  radial  fibers,  for  2  days  and  of  nerve- 
cells  for  from  3  to  6  days  in  pure  solution  of  potassium  bichromate  is 
better.  Still  better  results  are  obtained  by  the  vital  methylene-blue 
staining  (p.  42)  but  this  requires  great  skill  for  correct  orientation. 

No.  180. — Fresh  elements  of  the  retina. — Select  the  warm  eyes  of 
animals  just  killed.  Divide  the  eyeball  at  the  equator  and  carefully 
remove  the  vitreous  body  from  the  posterior  half;  cut  small  pieces  about 
3  mm.  square  from  the  wholly  transparent  retina  and  tease  gently  in  a 
drop  of  the  vitreous  humor  ;  place  two  thin  strips  of  paper  one  on  either 
side  of  the  preparation  (p.  53),  and  apply  a  cover-glass.  Isolated  ele- 
ments will  be  found  only  occasionally  here  and  there  ;  on  the  other  hand, 
very  good  surface  views  are  not  infrequently  obtained  in  which  the  rods 
and  cones  are  perceptible  in  optical  cross-section,  the  former  as  small,  the 
latter  as  large  circles.  If  at  the  same  time  a  little  piece  of  the  pigmented 
epithelium  has  been  transferred  to  the  slide,  the  regular  hexagonal  cells 
of  the  same  can  be  plainly  seen  with  the  low  power.  The  light  spots  in 
these  cells  are  their  nuclei  (Fig.  16).  These  cells  are  very  unstable  and 
soon  lose  their  sharp  contours  ;  molecular  motion  of  the  pigment  granules 
may  be  very  frequently  observed. 

No.  181. — The  best  method  for  isolating  the  elements  of  the  retina 

*  Among  mammals  only  the  ape  possesses  a  yellow  macula  and  a  central  fovea  ;  but  the 
majority  of  mammals — insectivora  and  certain  rodents  excepted — have  an  "area  centralis," 
without  yellow  pigmentation,  but  similar  in  structure  to  the  macula.  A  simple  or  multiple 
fovea  is  always  present  in  birds  and  reptiles ;  a  fovea  has  also  been  found  in  bony  fishes. 


432  HISTOLOGY. 

is  the  following  :  Place  the  unopened  eye,*  freed  from  fat  and  muscle,  in 
I  per  cent,  osmium  solution.  In  twenty-four  hours  cut  the  eye  open  at 
the  equator  and  for  maceration  place  it  for  two  or  three  days  in  distilled 
water  ;  then  with  scissors  cut  out  a  piece  of  the  retina  about  2  mm. 
square  and  tease  it  in  a  drop  of  water ;  the  preparation  may  be  stained 
under  the  cover-glass  with  picrocarmine  (p.  53)  and  mounted  in  dilute 
glycerol.  With  the  high  power,  in  addition  to  many  fragments  the  source 
of  which  is  not  always  to  be  determined  with  certainty,  elements  like 
those  pictured  in  Fig.  323  may  be  found. 

No.  182. — Corneal  spaces  and  canaliculi. — Select  an  eye  as  fresh  as 
possible  ;  of  the  eyes  of  animals,  that  of  the  ox  is  the  most  suitable  ;  with 
a  scalpel  vertically  applied  scrape  away  the  epithelium  of  the  cornea  ; 
spray  the  denuded  surface  with  distilled  water  ;  cut  through  the  eye  in 
front  of  the  insertion  of  the  ocular  muscles  and  place  the  anterior  segment 
containing  the  entire  cornea  down  on  the  epithelial  side  ;  then  with  for- 
ceps and  scalpel  remove  the  ciliary  body,  the  lens,  and  the  iris,  so  that 
only  the  anterior  portion  of  the  sclera  and  the  cornea  remain,  which  are 
to  be  placed  in  40  c.c.  of  a  i  per  cent,  solution  of  silver  nitrate.  The 
whole  is  then  stood  in  the  dark  for  from  three  to  six  hours,  after  which 
the  object  is  transferred  to  50  c.c.  of  distilled  water  and  exposed  to 
sunlight  (see  further,  p.  45).  Harden  the  object  in  50  c.c,  of  gradually 
strengthened  alcohols  and  cut  horizontal  sections,  which  are  most  easily 
obtained  if  the  cornea  is  held  over  the  left  index-finger.  It  is  best  to  take 
the  sections  from  the  posterior  surface  of  the  cornea,  since  the  spaces 
and  canaliculi  are  more  regular  there.  The  sections  may  be  stained  in 
Hansen's  hematoxylin  (p.  38)  and  mounted  in  xylol -balsam.  The 
pictures  are  negative,  the  spaces  and  canaliculi  white  on  a  brown  or 
brown-yellow  ground  (Fig.  314).  Carefully  examine  the  usually  some- 
what thinner  margins  of  the  section  ;  in  sections  stained  with  hema- 
toxylin the  large  nuclei  of  the  fixed  corneal  corpuscles  are  a  dull  blue  ; 
the  contours  of  the  cells  can  seldom  be  perceived. 

No.  183. — Fixed  corneal  corpuscles  by  the  gold  method. — The  method 
described  on  page  47  is  to  be  somewhat  modified,  as  follows  :  Express 
the  juice  from  a  fresh  lemon  ;  filter  it  through  flannel.  Kill  the  animal, f 
cut  out  the  cornea  and  place  it  for  five  minutes  in  the  lemon  juice,  in  which 
it  becomes  transparent ;  wash  it  in  5  c.c.  of  distilled  water  for  one 
minute  ;  transfer  it  to  10  c.c.  of  gold-chlorid  (p.  23)  solution  and  place 
it  in  the  dark  for  fifteen  minutes.  Then  with  glass  rods  transfer  the 
cornea  to  10  c.c.  of  distilled  water  for  one  minute,  then  to  50  c.c.  of  dis- 

*  It  is  advisable  to  select  the  eyes  of  small  animals — e.  g. ,  a  small  water  salamander 
(triton  tffiniatus) — in  which  the  sclera  is  thin  fand  allows  the  osmium  solution  to  penetrate 
easily.  For  such  an  eye  i  or  2  c.c.  of  the  solution  will  be  sufficient.  The  form  of  the  rods  is 
quite  different  from  those  of  mammals  ;  they  are  thick  and  are  provided  with  long  outer  seg- 
ments ;  the  cones  are  small. 

t  Frogs  are  especially  recommended  ;  their  corneal  canaliculi  are  very  regular  and  their 
posterior  corneal  lamellre  easily  detached. 


THE    ORGAN    OF    VISION.  433 

tilled  water,  to  which  2  drops  of  acetic  acid  have  been  added,  and  expose 
it  to  daylight ;  in  from  twenty-four  to  forty-eight  hours  the  reduction  is 
completed  {cf.  p.  48).  The  object  is  then  placed  in  10.  c.c.  of  70  per 
cent,  alcohol  (in  the  dark)  ;  on  the  following  day  cut  out  a  little  piece  of 
the  cornea,  and  with  needle  and  scalpel  placed  at  the  edge  separate  thin 
lamellae  from  the  posterior  surface;  with  a  little  attention  this  can  be 
successfully  done  without  much  trouble.  The  lamellae  mounted  in  xylol- 
balsam  furnish  very  beautiful  pictures  (Fig.  315). 

No.  184. — Very  beautiful  preparations  of  the  corneal  canaliculi  -ax^ 
obtained  by  the  method  o{  Drascli.  The  objects  are  not  to  betaken  from 
the  animal  recently  killed,  but  twelve  or  twenty-four  hours  after  death, 
during  which  time  the  cadaver  must  be  kept  in  a  cool  place.  Small 
pieces  of  the  cornea  are  to  be  cut  out,  about  6  mm.  square,  placed  in  5 
c.c.  of  I  per  cent,  gold-chlorid  solution  plus  5  c.c.  of  distilled  water,  and 
stood  in  the  dark  for  one  hour  ;  during  this  time  frequently  stir  the  fluid 
with  a  glass  rod.  With  glass  rods  transfer  the  pieces  to  30  c.c.  of  dis- 
tilled water,  in  which  they  should  remain  (in  the  dark)  for  from  eight  to 
sixteen  hours.  They  are  then  to  be  transferred  to  25  c.c.  of  distilled 
water  plus  5  c.c.  of  formic  acid  and  exposed  to  daylight.  When  the 
reduction  is  completed  (p.  47)  the  dark-violet  pieces  are  to  be  hard- 
ened in  gradually  strengthened  alcohols  and  in  about  six  days  thin 
sections  parallel  to  the  surface  can  be  cut  and  mounted  in  xylol-balsam. 

No.  185. — Nerves  and  blood-vessels  of  the  fresh  cornea. — Select  the 
eye  of  an  ox  and  cut  out  the  cornea  with  the  adjoining  portion  of  the 
sclera,  extending  from  the  limbus  to  the  insertion  of  the  ocular 
muscles ;  with  scalpel  and  forceps  remove  the  ciliary  body,  iris,  and 
lens,  immediately  cut  out  a  quadrant  of  the  cornea,  place  it  with  the  epi- 
thelial side  up  on  a  slide  and  apply  a  cover-glass  ;  add  a  few  drops  of 
the  vitreous  humor.  The  very  thick  preparation  must  be  examined 
with  a  low  power.  When  the  superficial  strata  of  the  cornea  are  in 
focus  the  loop-shaped  blood-vessels  can  be  seen  at  the  scleral  margin  ; 
the  majority  still  contain  blood  corpuscles.  MeduUated  nerve-fibers  are 
found  here,  as  well  as  in  the  deeper  strata  ;  they  are  arranged  in  big 
bundles  and  can  be  traced  only  for  a  short  distance  within  the  cornea. 
The  elongated  pigment  streaks  found  in  the  eye  of  the  ox  have  no 
relation  to  the  nerves. 

This  method  is  not  serviceable  for  the  exhibition  of  the  finer  distri- 
bution of  the  nerves. 

No.  186. — Nerves  of  the  cornea. — (d)  Gold  method. — Cut  out  the 
cornea  twelve  or  twenty-four  hours  after  death,  detach  the  ciliary  body 
and  the  iris,  and  treat  it  according  to  the  method  given  in  No.  184. 
When  the  hardening  is  completed  cut  horizontal  sections,  which  contain 
the  epithelium  and  the  uppermost  lamellae  of  the  cornea,  and  vertical 
sections  through  the  thickness  of  the  cornea.  Mount  in  xylol-balsam 
(Fig.  330). 

[b^  MetJiylene-bhie  staining. — Kill  a  rabbit ;  remove  the  entire  eye- 
28 


434 


HISTOLOGY. 


ball,  free  it  from  the  attached  remnants  of  ocular  muscles  and  connective- 
tissue,  place  it  in  a  watch-glass  and  with  a  sharp  scalpel  make  a  deep 
incision  at  the  equator  through  all  the  coats  of  the  eye  ;  the  escaping 
vitreous  humor  is  caught  in  the  watch-glass.  Then,  beginning  at  the 
incision  made,  cut  out  the  entire  cornea,  place  it  on  a  slide  with  the  con- 
cave surface  upward  and  with  the  handle  of  the  scalpel  scrape  off  the 
ciliarv  body,  iris,  and  lens,  which  is  easily  done  ;  transfer  the  cornea  thus 
cleansed  to  a  second  watch-glass  containing  from  3  to  lO  drops  of  the 
vitreous  humor  and  from  3  to  4  drops  of  a  0.06  per  cent,  methylene-blue 
solution  (p.  42).  The  concave  surface  of  the  cornea  should  be  upper- 
most and  covered  by  the  staining  fluid. 

The  time  required  for  staining  cannot  be  given  with  certainty  ;  there- 
fore it  is  advisable  after  several  hours  to  place  the  cornea  with  the  convex 
surface  up  on  a  clean  slide  and,  without  a  cover-glass,  to  examine  it  with 
the  low  power  ;  if  it  is  not  sufficiently  stained  return  it  to  the  watch-glass 
and  examine  it  again  in  about  ten  minutes. 

So  soon  as  the  nerves  can  be  distinctly  seen  the  cornea  is  to  be 
transferred  for  from  eighteen  to  twenty  hours  to  20  c.c.  of  the  ammonia 
solution  (p.  26);  then  cut  out  a  quadrant  and  mount  it  in  dilute  glycerol, 
to  which  a  drop  of  the  ammonia  solution  has  been  added  ;  after  being 
kept  in  the  dark  for  twenty-four  hours  the  preparation  is  sufficiently 
transparent  and  can  be  investigated  with  the  high  power. 

No.  187. — Lens-fibers. — Cut  open  the  eyeball  back  of  the  equator; 
remove  the  vitreous  body  and  lens  ;  the  pigment  covering  the  ciliary 
processes  remains  attached  to  the  margin  of  the  lens.  Loosen  the  lens 
from  the  vitreous  body  and  place  it  in  50  c.c.  of  Ranvier's  alcohol  (p.  20). 
In  about  two  hours  thrust  needles  into  the  anterior  and  the  posterior 
surface  of  the  lens  and  strip  the  capsule  from  a  small  area ;  this  is  easily 
done  ;  if  lens-fibers  are  attached  to  the  capsule  it  does  not  matter.  On 
pricking  the  lens  a  turbid  white  fluid  escapes  ;  shake  the  alcohol  and  let 
the  lens  remain  in  it  for  from  ten  to  forty  hours.  At  the  expiration  of 
this  time  the  lens  can  be  easily  separated  into  shell-like  pieces.  Tease  a 
small  strip  of  one  of  these  pieces  in  a  small  drop  of  distilled  water 
on  a  slide.  Apply  a  cover-glass,  taking  care  to  avoid  pressure  ;  if  it  is 
desired  to  preserve  the  fibers,  stain  with  picrocarmine  (p.  53),  staining 
usually  occurs  in  a  few  minutes,  and  mount  in  dilute  acidulated  glycerol 
(Fig.  327  A). 

-^Q  J  8  8. — Lens  fibers  in  transverse  section. — Place  a  lens  in  50  c.c. 
of  0.05  per  cent,  chromic  acid  (p.  32).  A  wad  of  cotton  must  be  placed 
on  the  bottom  of  the  bottle  or  the  lens  will  adhere  to  the  glass  and  burst. 
This  may  also  be  prevented  by  frequently  shaking  the  bottle.  In  from 
twenty-four  to  forty-eight  hours,  with  a  needle  break  the  lens  into  shell- 
like pieces  ;*   transfer  them  after  ten  or  fifteen  hours  to  30  c.c.  of  70  per 


*  The  shell-like  fragments  obtained  in  maceration  experiments  are  the  source  of  the  false 
doctrine  of  the  concentric  stratification  of  the  lens ;  they  are  simulated  also  in  meridional  sec- 
tions ;  that  which  is  here  visible  are  individual yf^irrj,  not  lamella.     Equatorial  sections  through 


THE    ORGAN    OF    VISION.  435 

cent,  alcohol,  which  is  to  be  replaced  on  the  following  day  by  an  equal 
quantity  of  90  per  cent,  alcohol.  With  the  scissors  cut  the  pieces 
through  in  the  region  of  the  equator,  and  so  embed  them  in  liver  that 
the  first  sections  will  pass  through  the  zone  lying  next  to  the  equator. 
If  the  sections,  which  need  not  be  very  thin,  have  passed  through  the 
fibers  transversely  they  will  appear  as  sharply  defined  hexagons  ;  if,  on 
the  contrary,  the  sections  are  oblique  the  single  fibers  will  appear  to  be 
separated  from  one  another  by  irregular  zigzag  lines  ;  they  may  even  be 
cut  partially  lengthwise.  The  sections  are  to  be  transferred  directly 
from  the  blade  to  the  slide  and  mounted  in  dilute  glycerol  (Fig.  327  B). 

No.  189. — The  lens-capsule  and  the  lens  epitJieluim. — Place  the 
eyeball  free  from  muscle  and  fat  in  100  or  200  c.c.  of  Miiller's  fluid 
(p.  33).      Treat  it  further  as  follows  : 

{a)  Surface  viezu  of  the  lens-capsnle  and  epithelhun. — After  two  or 
three  days  cut  the  eye  open,  take  out  the  lens,  remove  as  far  as  possible 
the  zonula  fibers,  and  with  small  forceps  strip  off  a  piece  of  the  anterior 
lens-capsule  ;  place  it  for  about  five  minutes  in  a  watch-glass  with  dis- 
tilled water,  which  is  to  be  changed  once,  then  stain  it  in  Hansen's  hema- 
toxN'lin  (p.  38)  ;  mount  in  xylol-balsam.  The  capsule  is  stained  a 
homogeneous  hght  blue  ;  the  nuclei  and  contours  of  the  epithelial  cells 
are  very  sharp  (Fig.  328  C^.  If  it  is  desired  to  obtain  the  lens-capsule 
alone  strip  off  a  portion  of  the  posterior  lens-capsule. 

{b)  Sections  of  the  capsule  and  epitheliuvi. — Let  the  eyeball  remain 
in  Miiller's  fluid  for  two  weeks  ;  remove  the  lens,  wash  it  for  one  hour  in 
running  water  and  harden  it  in  50  c.c.  of  gradually  strengthened  alcohols 
(p.  35).  Embedding  in  celloidin  is  advisable.  Cut  meridional  sections 
through  the  anterior  surface  and  through  the  equator  of  the  lens,  which 
are  to  be  stained  with  Hansen's  hematoxylin  and  mounted  in  xylol- 
balsam  (Fig.  328  D),  and  equatorial  sections  that  begin  at  the  posterior 
pole.  The  sections  through  the  anterior  surface  show  beautifully  the 
attachment  of  the  lens-fibers  to  the*  rays  of  the  lens-star.  Since  the  firm 
core  is  very  difficult  to  cut,  it  is  advisable  when  this  part  of  the  lens  is 
reached  to  loosen  and  extract  the  core  by  means  of  a  small  knife  and 
to  fill  the  cavity  with  celloidin. 

No.  190. — The  blood-vessels  of  the  eye. — For  this  purpose  surface 
prepartions  are  especialh^  suitable.  On  opening  a  fresh  eye  at  the  equator 
the  course  of  the  central  artery  of  the  retina  is  macroscopically  percep- 
tible. For  the  exhibition  of  the  blood-vessels  of  the  choroid  place  an 
eyeball  completely  freed  from  attached  muscle  and  fat  on.  a  small  glass 
funnel,  which  has  been  thrust  into  a  low  glass  bottle,  and  with  scissors 
and  forceps,  beginning  at  the  equator,  carefully  dissect  off  the  sclera. 
With  a  little  practice  the  entire  sclera  can  be  removed  from  a  little  behind 
the  ora  serrata  up  to  the  optic  entrance  without  injury  to  the  choroid  ;  care 


the  lens  exhibit  the  image,  not  of  an  onion,  but  of  an  orange, — of  radial\a.vat\\x.  The  falling 
apart  in  shells  is  owing  to  the  fact  that  lens-fibers  of  approximately  the  same  age  also  possess 
like  consistence,  like  physical  and  chemic  nature. 


436  HISTOLOGY. 

must  be  taken  not  to  tear  it.  (Beginners  should  be  content  to  remove 
only  one  quadrant  of  the  sclera.)  All  the  firmer  cords  of  attachment  (the 
ven^  vorticosae)  between  the  sclera  and  the  choroid  must  be  cut  through. 
Then  by  careful  brushing  with  a  camel's-hair  pencil  moistened  in  water  re- 
move the  attached  portions  of  the  lamina  suprachorioidea  from  the  choroid  ; 
by  this  manipulation  the  course  of  the  larger  blood-vessels  is  brought 
to  view.  So  far  the  investigation  may  be  pursued  on  the  uninjected  eye 
(compare  Avith  178  a).  For  the  study  of  the  blood-vessels  of  the 
ciliary  body  and  the  iris  it  is  necessary  to  use  an  injected  eye,  divided 
anterior  to  the  equator,  fixed  in  Miiller's  fluid  and  hardened  in  alcohol. 
The  iris  and  the  ciliary  body  can  be  easily  stripped  from  the  sclera ;  re- 
move the  lens  and  then  mount  in  xylol-balsam.  Examine  at  first  with 
a  very  low  power. 

No.  191. — The  eyelid. — Fix  the  upper  eyelid  of  a  child  in  ca.  60  c.c. 
of  potassium-bichromate-acetic-acid  (p.  32)  for  from  i  to  3  days  and  after 
washing  for  3  hours  in  running  water  harden  in  ca.  50  c.c.  of  alcohols  of 
ascending  degrees  of  strength  (p.  35).  For  topographic  preparations 
(Fig.  331)  cut  thick  sections  ;  for  the  finer  details  (Fig.  37  C,  p.  92)  cut 
thin  sections.  Stain  with  Hansen's  hematoxylin  (p.  38)  and  mount  in 
xylol-balsam. 

No.  192.  —  TJie  lacrimal  glands. — The  lower  tear-gland  in  man 
can  be  easily  removed,  without  visible  external  injury,  from  the  fornix  of 
the  conjunctiva.  In  the  rabbit  this  gland  is  very  small  and  when  fresh 
resembles  pale  muscle  tissue.  It  must  not  be  confused  with  Harder's 
gland  lying  in  the  median  angle  of  the  eye.  Treat  like  No.  1 18  (p.  304). 
Small  pieces  i  mm.  square  can  be  used.  The  excretory  duct  and  the 
tubules  are  easily  seen  ;  difficult,  on  the  other  hand,  it  is  to  see  the  inter- 
calated tubules,  the  epithelium  of  which  varies  greatly  in  height  and 
occasionally  is  so  low  that  care  must  be  taken  not  to  confuse  them  with 
blood  capillaries  (Fig.  332). 


XI.  THE   ORGAN   OF   HEARING. 

The  organ  of  hearing  consists  of  three  divisions  ;  the  innermost,  the 
internal  ear,  encloses  the  end  apparatus  of  the  auditory  nerve  ;  the  other 
divisions,  the  middle  ear  and  the  exter7ial  ear,  are  only  accessory  ap- 
paratus. 

The  Internal  Ear. 

The  internal  ear  consists  of  two  membranous  saccules  lying  within 
the  bony  vestibule  (vestibulum),  that  communicate  with  each  other  by 
means  of  a  minute  canal,  the  ductus  tttriculo-saccularis.  The  one  saccule, 
the  utricle  (utriculus),  is  in  connection  with  membranous  tubules,  the  semi- 
circidar  canals  (ductus  semicirculares),  each  of  which  at  the  point  where 
it  opens  in  the  utricle  possesses  a  dilatation,  the  ampulla.     The  other  sac- 


THE    ORGAN    OF    HEARING.  437 

cule,  the  sacculus,  connects  by  means  of  the  ductus  rcuiiiois  with  a  long, 
spirally  wound,  membranous  tube,  the  cochlea  (ductus  cochlearis). 

The  sacculus  and  the  utriculus,  the  semicircular  canals  and  the 
cochlea  are  called  the  membranous  labyrinth.  This  is  enclosed  within 
the  petrous  bone  in  cavities  having  similar  outlines,  the  bo7iy  labyrinth, 
which  it  does  not  completely  fill.  The  unfilled  space  is  occupied  by  a 
watery  fluid,  tho.  perilymph.  A  similar  fluid,  the  eudolymph,  is  contained 
in  the  interior  of  the  membranous  labyrinth. 

The  saccules  and  the  semicircular  canals  agree  in  structure,  but  the 
cochlea  is  so  essentially  different  that  it  requires  a  separate  description. 

THE    SACCULE,  THE    UTRICLE,  AND    THE    SEMICIRCULAR    CANALS. 

The  walls  of  these  structures  consist  of  three  layers.  The  outermost 
is  a  connective-tissue  layer  rich  in  elastic  fibers  ;  this  is  followed  within  by 
a  delicate  basal  membrane  beset  with  minute  excrescences,  which  on  its 
inner  surface  is  covered  by  a  simple  squamous  epithelium.  This  simple 
structure  undergoes  alteration  at  the  places  where  the  filaments  of  the 
auditory  nerve  are  distributed,  which  in  the  saccule  and  the  utricle  are 
named  the  maculce,  in  the  ampullje  of  the  semicircular  canals  the 
cristcB  acnsticce.  The  connective  tissue  and  basal  membrane  here  become 
thicker ;  the  squamous  epithelium  already  at  the  periphery  of  the 
maculae  and  cristse  becomes  transformed  into  a  cylinder  epithelium  with 
a  cuticular  border,  and  this  passes  into  the  neuro-epithelium  of  the 
macular  and  cristx.  The  neuro-epithelium  likewise  is  a  simple  layer  and 
consists  of  two  kinds  of  cells  :  {\)  fiber-cells,  tall,  slender  elements  occu- 
pying the  entire  height  of  the  epithelium,  slightly  expanded  at  the  upper 
as  well  as  at  the  lower  end,  which  contain  an  oval  nucleus  ;  they  are 
the  supporting  elements  ;  (2)  hair-cells,  cylindrical  elements  occupying 
only  the  upper  half  of  the  epithelium,  which  in  their  lower,  rounded 
division  contain  a  large,  spherical  nucleus  and  on  their  free  surface  bear  a 
bundle  of  long,  delicate,  agglutinated  filaments,  the  "auditory  hair." 
The  hair-cells  are  the  terminal  apparatus  of  the  auditory  nerve.  The 
nerve-fibers  of  the  ramus  vestibularis  nervi  acustici  are  in  connection 
with  the  hair-cells  in  this  way  :  on  entering  the  epithelium  the  nerve- 
fibers  lose  their  medullary  sheath,  divide,  and  as  naked  axis-cylinders 
ascend  to  the  base  of  the  hair-cells  ;  there  each  fiber  divides  into  three 
or  four  varicose  twigs,  that  run  horizontally  beneath  several  hair-cells, 
parallel  to  the  surface  of  the  epithelium,  and  finally  turn  upward  and 
terminate  in  contact  with  the  lateral  surface  of  a  hair-cell  in  a  free 
pointed  end.*     During  their  horizontal  course  they  send  upward  a  few 

*  The  horizontal  branches  interlace  and  form  a  small  but  close  "  lattice-work,"  that  also 


438  HISTOLOGY. 

twigs,  that  in  the  same  manner  end  in  contact  with  the  hair-cells.     These 

ends  do  not  reach  to  the  surface  of  the  epithelium.      The  free  surface  of 

the  neuro-epithelium  is  covered  by  a  continuation  of  the  cuticular  border, 

a  "  limitans,"    which   is    perforated   by   the   auditory 

J^  hairs.      The  maculse  acusticae  are  covered  by  a  soft 

^     r-^  substance  (a  cuticula  ?),  in    which    innumerable  pris- 

<S^   °   0  matic  crystals  of  calcium  carbonate,  the  otoliths,  from 

o    r^  I  to  I  5  p-  in  size,  are  embedded  ;  together  they  form 

the  "  otoconia,"   the  auditory  sand.      On  the    cristae 

Fig.  333— Otoliths  .  ... 

FROM  THE  sacculus     acusticse  thc  so-called  cupicta  occurs,  m  iresh  prepara- 

OF  AN  Infant.     X         . 

560.    Technic  No.     tions   an    invisible  jelly,   that    on    the    application    of 

fixation  fluids  coagulates  and  thus  becomes  visible. 

By  means   of  strands   of  connective  tissue  (ligamenta  sacculorum 

at  ductuum)  the  saccules  and  the  semicircular  canals  are  secured  to  the 

the  bony  labyrinth,  the  inner  surface  of  which  is  covered  with  a  thin 

periosteum  and  flattened  connective-tissue  cells. 

THE    COCHLEA. 

The  membranous  cochlea,  the  ductus  cochlearis,  does  not  entirely  fill 
the  space  within  the  bony  cochlea.  It  lies  with  one  wall  in  contact  with 
the  outer  wall*  of  the  bony  cochlea  (Fig.  334  ) ;  the  upper  or  vestibular 
wall,  the  vestibular  inembj'aiie  (Reissner),  bounds  the  scala  vestibuli ;  the 
lower  or  tympanic  wall,  the  uienibranous  spiral  lamina,  is  directed  toward 
the  scala  tympani.  The  angle  in  which  the  vestibular  and  the  tympanic 
wall  meet  lies  on  the  free  end  of  the  osseous  spiral  lamina.  There  the 
periosteum  and  the  connective  tissue  of  the  ductus  cochlearis  are  espe- 
cially well  developed  and  form  an  eminence,  the  limbiis  spiralis,  which 
rests  with  a  broad  base  on  the  bony  spiral  lamina,  slopes  upward  and 
terminates  in  a  sharp  edge.  This  edge  is  called  the  labium  vestibidarc, 
the  free  margin  of  the  bony  spiral  lamina  is  called  the  labium  tympani- 
cwn,\  between  the  two  runs  the  sulcus  spiralis  (Fig.  341).  The  inner  sur- 
faces of  the  ductus  cochlearis  are  covered  by  an  epithelium  of  very  different 
nature  in  the  different  localities  ;  the  outer  surfaces,  toward  the  scala 
vestibuli  and  the  scala  tympani,  are  covered  by  a  delicate  continuation  of 

by  the  application  of  other  methods  than  that  of  Golgi  appears  to  consist  of  a  peculiar  layer  of 
strongly  refracting  granules.  The  granules  are  the  varicosities  and  the  optical  cross-sections 
of  the  horizontal  fibers. 

*  I  here  follow  the  customary  description,  in  which  the  cochlea  is  placed  in  such  a  manner 
that  the  base  is  directed  downward,  the  summit  upward;  accordingly  "inner"  is  toward  the 
axis  of  the  cochlea,  "  outer"  toward  the  periphery. 

f  The  names  were  bestowed  at  the  time  in  which  the  limbus  spiralis  was  accounted  as 
part  of  the  lamina  spiralis  ossea. 


THE    ORGAN    OF    HEARING. 


439 


the  periosteum  which  clothes  both  scaL'e.  On  the  outer  wall  of  the  cochlea 
the  periosteum  becomes  greatly  thickened  and  in  cross-section  appears 
as  a  huge  crescentic  mass,  the  ligmncnhini  spiralc,  that  extends  above 
and  below  the  attached  surface  of  the  ductus  cochlearis  (Fig.  335). 

The  ))iimitc  structure  of  the  outer  and  the  vestibular  wall  of  the 
membranous  cochlea  is  comparativeh'  simple,  of  the  tympanic  wall,  on 
the  other  hand,  is  extremely  complicated. 

The  outer  wall  and  the  spiral  ligamcut  together  consist  of  epithelium 
and  connective  tissue.  The  latter,  next  to  the  bone,  is  a  dense  fibrous 
tissue  (the  periosteum)  and  this  passes  into  a  loose  connective  tissue 
which    contributes   the   chief  bulk   of   the   spiral    ligament.      The    epi- 


Modiolus. 


Scala  vestibuli. 


Scala  tympani. 


"  Ramus  cochlearis 


)      of  the 


~  Ramus  vestibularis  J  ^custicus. 


Meatus  acusticus  internus. 


Fig.  334.  —  Horizontal  Sectiox  through  the  anterior  portion  of  the  Petrous  Bone  of  a  Kitten. 
X  8.  The  ductus  cochlearis,  .r,  fell  ^v^thin  the  plane  of  the  section  five  times.  The  variable  color  of  the 
bone  is  owing  to  the  incomplete  penetration  of  the  fixation  medium.     Technic  No.  195. 


thelium  consists  of  a  layer  of  cubical  epithelial  cells.  A  dense  network 
of  blood-vessels,  the  stria  vascularis,  occupies  three-fourths  of  the  height 
of  the  outer  cochlear  wall,  and  downwards  is  bounded  by  a  vein  that 
projects  farther  into  the  lumen  of  the  cochlea,  the  vas  prominens  (Fig. 
335).  The  capillaries  of  the  stria  vascularis  lie  close  beneath  the  epi- 
thelium (Fig.  341)  ;  they  are  the  source  of  the  endolymph. 

The  vestibular  zvall,  membrana  vestibularis  (Fig.  335),  consists  of  a 
process  of  the  periosteum  of  the  scala  vestibuli,  that  is,  of  delicate  fibrous 
connective  tissue  and  flattened  cells,  which  on  the  surface  turned  toward 
the  ductus  cochlearis  is  clothed  with  a  simple  layer  of  poh'gonal  epi- 
thelial cells. 

The  tympanic  ■itv?// consists  of  two  divisions  (i),  the  limbus  spiralis 


440 


HISTOLOGY. 


with  the  free  margin  of  the  osseous  spiral  lamina,  and  (2)  the  lamina 
spiralis  membranacea. 

The  limbiis  spiralis  consists  of  a  compact  connective  tissue,  rich  in 


Blood-vessels. 


Ganglion  spirale. 


Scala  vestibuli. 


Ductus 
cochlearis. 


Vas  prominens. 


'^  Ligamentum  spirale. 


Scala  tympani. 


Lamina  spiralis  ossea. 


Lamina  spiralis  membranacea. 


Fig- 335- — The  Portion   or   Figure  334  marked  "Scala   vestibuli"  and    "Scala  tympani."     X  50. 

Technic  No.  195. 

spindle-shaped  cells,  which  below  is  grown  together  with  the  periosteum 
of  the  lamina  spiralis  ossea,  on  its  free  surface  is  beset  with  peculiarly 
shaped  papillse.  They  have  the  form  of  irregular  hemispheres  ;  toward 
the    labium    vestibulare   they    develop    into    small,    elongated    plates, 


Labium  tympanicum. 


Labium  vestibulare. 


^^^\ ": 


Foramina  nervina. 

7 

Zona  perforata. 
-   Auditory  teeth. 


'o      U  y;^Z^:zrz — —     PapUliB. 

Fig.  336.— a  Surface  view  of  the  Lamina  Spiralis  of  a  Cat.  X  240.  The  vestibular  lamina  is  seen  from 
above;  betvi'een  the  auditory  teeth  two  nuclei  of  the  epithelial  cells  are  visible.  On  the  left  of  the  picture 
the  plane  of  the  auditory  teeth  is  in  focus,  on  the  right,  the  plane  of  the  zona  perforata.     Technic  No.  194. 


Huschke's  auditory  teeth  (Fig.  336  and  Fig.  339),  that  lie  in  a  simple  row 
beside  one  another.  The  surface  of  the  limbus  is  covered  by  a  simple 
layer  of  much  flattened  epithelial  cells,  which  at  the  edge  of  the  labium 


THE    ORGAN    OF    HEARING. 


441 


vestibulare  passes  into  the  cubical  epithelium  of  the  sulcus  spiralis  (Fig. 

339.  ^)- 

The  upper  surface  of  the  free  margin  of  the  osseous  spiral  lamina  is 

perforated  by  a  single   row  of  slit-like  openings,  the  forauiina  ncrvina 

(Fig.   336)   through  which  the  nerves  enclosed  in 

the  bony  lamina  emerge,   to  penetrate  within  the 

epithelium    of   the    lamina    spiralis    membranacea. 

Therefore  this  zone  of  the  osseous  spiral  lamina  is 

called  zona  perforata  (Habenula). 

The  7)iembranoiis  spiral  lamina  (lamina  spiralis 
membranacea)  consists  of  (i)  the  menibrana  basilaris, 
an  extension  of  the  limbus  spiralis  and  of  the  peri- 
osteum of  the  osseous  spiral  lamina,  (2)  the  tym- 
panal lamella,  a  process  of  the  periosteum  of  the 
scala  tympani,  which  clothes  the  lower  surface  ot 
the  basilar  membrane,  and  (3)  the  cpitliclium  of  the 
ductus  cochlearis,  which  rests  upon  the  upper  sur- 
face of  the  basilar  membrane. 

The  membrana  basilaris  consists  of  a  structureless  lamella,  which 
contains  rigid,  perfectly  straight  fibers,  extending  from  the  labium  tym- 
panicum  to  the  spiral  ligament,  and  also  oblong  nuclei.  This  gives  to 
the  membrane  a  finely  striated  appearance  (Fig.  337,/)- 


Fig.  337. — Surface  view  of 
THE  Lamina  Spiralis 
Membranacea  of  a 
Cat.  X  240.  Strata  of 
the  zona  pectinata  drawn 
with  change  of  focus. 
e.  IndiSerent  epithelium 
(cells  of  Claudius)  of  the 
ductus  cochlearis  in  fo- 
cus; /,  the  fibers  of  the 
membrana  basilaris  in 
focus;  h,  the  nuclei  of  the 
tympanal  lamella  in  fo- 
cus.    Technic  No.  194. 


Cells  of  Claudius. 

Fibers. 

Outer  hair-cells. 

Pillar-cells. 

Inner  hair-cells. 


\0 


Zona  pectinata.") 

rim. 
Zona  tectoria.    j 

Labiiun  tympanicum. 
Labium  vestibulare. 


Ganglion  spirale.   — 


Fig.  338. — Lamina  Spiralis  of  a  Cat,  seen  from  the  Vestibular  Surface.  The  membrana  tectoria  has 
been  removed.  X  50.  lo.  Lamina  spiralis  ossea,  the  inner  half  fractured  and  broken  at  several  places; 
at  the  posterior  border  of  the  same  cells  of  the  spiral  ganglion  project  forth.  Ivi.  Lamina  spiralis  mem- 
branacea. The  cells  of  Claudius  have  partly  fallen  off,  so  that  the  fibers  of  the  membrana  basOaris  are 
visible  as  a  dehcate  striation.    Technic  No.  194. 


The  tympanic  lamella  consists  of  a  delicate  connective  tissue  contain- 
ing spindle-cells,  the  fibers  of  which  are  disposed  vertically  to  the  fibers 
of  the  basilar  membrane  (Fig.  337,  b^. 

The  epithelium  of  that  half  of  the  membranous  spiral  lamina  toward 


442 


HISTOLOGY. 


the  axis  of  the  cochlea  is  differentiated  into  the  neuro-epithehum  of  the 
spiral  organ  (organon  spirale,  Corti),  while  that  occupying  the  outer  half, 
toward  the  spiral  ligament,  consists  of  indifferent  epithelial  elements. 
Therefore  the  membranous  spiral  lamina  is  divided  into  two  zones  :  an 
inner,  occupied  by  the  spiral  organ,  zona  iecta,  and  an  outer,  zona 
pectinata,  so  named  because  of  the  striations  of  the  basilar  membrane 
shimmering  through  it. 

The  most  remarkable  elements  of  the  spiral  organ  are   the  pillar- 
cells,  peculiarly  shaped,  for  the  greater  part  rigid  structures,  arranged  in 


Nerve 


Pillar-cells. 


Fig.  339. — Scheme  of  the  Structure  of  the  Tympanic  Wall  of  the  Duct  of  the  Cochlea.  A.  View  from 
the  side.  B.  View  from  the  surface.  In  the  latter  the  free  surface  is  in  focus.  It  is  evident  that  the  epi- 
thelium of  the  sulcus  spiralis,  lying  in  another  plane,  as  weU  as  the  cells  of  Claudius,  can  only  be  distinctly 
shown  by  depressing  the  tube.  The  membrana  tectoria  is  not  drawn.  The  spiral  nerve-bundles  are  in- 
dicated by  dots. 


two  rows  through  the  entire  length  of  the  cochlea.  The  inner  row  of 
pillar-cells  form  the  inner  pillars,  the  outer  row,  the  outer  pillars  (Fig. 
339).  The  two  rows  of  pillars  are  obliquely  inclined  toward  one  another 
and  form  an  arch,  the  arciis  spiralis,  which  spans  a  triangular  space,  the 
tunnel,  the  base  of  which  is  directed  toward  the  basilar  membrane.  The 
tunnel  is  nothing  else  than  a  very  large  intercellular  space,  that  is  filled 
with  a  soft  mass,  with  intercellular  substance.  Regarding  the  histology  of 
the  pillar-cells  the  following  details  are  to  be  considered  :  The  inner 
pillar-cells  are  rigid  bands,  in  which  a  tliree-sided,  expanded  foot,  a  slender 


THE    ORGAN    OF    HEARING.  443 

body,  and  a  concave  head,  with  the  concavity  directed  outward,  arc  distin- 
guished. The  head  is  furnished  with  a  small  process,  the  "head-plate" 
(Fig.  339).  The  body  and  foot  of  the  cell  are  surrounded  by  a  scant 
amount  of  protoplasm,  that  only  to  the  outer  side  of  the  foot  in  the 
vicinity  of  the  nucleus  is  present  in  somewhat  larger  amount.  The 
outer  pillar-cells  exhibit  the  same  details,  excepting  that  the  portion  con- 
taining the  nucleus  lies  to  the  inner  side  of  the  foot ;  the  rounded  articu- 
lar head  rests  in  the  concave  facet  of  the  head  of  the  inner  pillars,  the 
broader  head-plate  is  covered  for  the  greater  part  by  the  head-plate  of 
the  inner  pillars.*  To  the  inner  side  of  the  inner  pillars  lies  a  simple  row 
of  cells,  the  inner  hair-cells,  short  cylindrical  elements  that  do  not  extend 
to  the  basilar  membrane  ;  they  possess  a  rounded  base  and  about  forty 
long,  stiff  hairs  on  their  free  surface.  To  the  inner  side  of  the  inner  hair- 
cells  lies  the  cubical  epithelium  of  the  sulcus  spiralis  internus.      On  the 


np 

K 

^".         ,—  '■/' 

N^^ 

hip 

'    ,// 

Fig.  340. — From  the  Lamina  Spiralis  Membranacea  of  a  Cat.  X  240.  A.  Outer  pillar-cells;  k.  head- 
plates  of  the  same,  upper  surface  in  focus  ;  ap.  body  and  lower  end  of  the  same  sketched  under  gradual  de- 
pression of  the  tube  ;  kip,  portions  of  the  head-plates  of  inner  pillar-cells.  B.  U.  Labium  tympanicum, 
partly  covered  by  the  epithehum  of  the  sulcus  spiralis  ;  ih.  inner,  ah,  outer  hair-cells,  between  these  the  phal- 
anges, ph,  forming  the  membrana  reticularis  ;  ap,  head-plates  of  the  outer,  ip,  of  the  inner  pillar-cells.  Tech- 
nic  No.  194. 

outer  side  of  the  outer  pillars  lie  the  onter  hair-cells  ;  they  resemble  the 
inner  hair-cells,  but  possess  hairs  that  are  one-third  shorter  and  are  char- 
acterized by  a  dark  body  situated  in  the  upper  half  of  the  cell,  the  spiral 
body  (Hensen).t  The  outer  hair-cells  are  arranged  not  in  one,  but  in 
several  (usually  four)  rows  ;  they  do  not  lie  in  contact  with  one  another, 
but  are  held  apart  by  Deiters' s  cells  ;  these  are  slender  cells,  each  of  which 
contains  a  rigid  filament  and  at  its  upper  end  supports  a  cuticnlar  process, 
that  has  the  shape  of  a  digital  phalanx.  The  free  spaces  between  the 
"  phalanges  "   are  occupied   by  the  upper  ends  of  the  outer  hair-cells  % 

*  The  nucleus-like  inclusion  found  in  the  heads  of  the  inner  and  the  outer  pillars,  also 
that  in  the  feet  of  the  latter,  has  no  relation  to  a  nucleus,  but  probably  is  of  a  horny  nature. 

I  In  the  scheme  (Fig.  339  A)  this  body  is  indicated  by  a  dark  spot  close  beneath  the 
auditory  hairs. 

X  The  inner  hair-cells  are  held  apart  from  one  another  by  short  processes  of  the  inner 
pillar-cells.     These  processes  are  not  shown  in  Fig.  339. 


444 


HISTOLOGY. 


(Fig.  340).  The  cells  of  Deiters  are  supporting  elements,  that  exhibit 
much  in  common  with  the  pillar-cells  ;  like  these  they  consist  of  a  rigid 
filament  and  a  protoplasmic  portion,  like  these  they  have  a  head-plate 
(named  phalanx).  The  difference  consists  only  in  this,  that  the  transfor- 
mation into  rigid  parts  is  not  so  far  advanced  in  the  cells  of  Deiters.  The 
phalanges  are  joined  to  one  another  and  form  a  beautiful  netted  mem- 
brane, the  membrana  reticularis. 

The  outer  hair-cells  do  not  extend  down  to  the  basilar  membrane, 
but  occupy  only  the  upper  half  of  the  spaces  between  the  cells  of  Deiters  ; 
the  lower  divisions   of  these  spaces   remain   unoccupied  and  are   called 


Membrana  tectoria. 


Capillaries  of  the  stria. 
( 


-,  Hair-cells. 

Labium  vestibulare.     Sulcus  spiralis.      ',     -J^^^T— 5;;;;^  ""Tells"'^  "celt^'^         ^ 


I  ^^1  ^   ^ 


Nerve-bundle.  Labium       Inner  Outer  Deiters's    Membrana     Tympanal 

tympanicum."" "^     -—^^  cells.         basilaris.         lameUa. 

Pillar-cells. 

Fig.  341. — Portion  of  Figure  335.     Magnified  240  times,     x.  Tunnel  traversed  by  nerve-fibers. 

Nuefs  Spaces,  or,  since  they  communicate  with  one  another,  the  space  of 
Nuel  (Fig.  339,  A).  The  latter  also  has  the  significance  of  an  intercel- 
lular space  and  communicates  with  the  tunnel. 

External  to  the  last  row  of  Deiters's  cells  lie  the  cells  of  Hensen, 
slender  cylinders,  that  gradually  decrease  in  height  and  pass  into  the  in- 
different epithelium  of  the  cochlear  duct,  the  elements  of  which,  so  far 
as  they  cover  the  basilar  membrane,  are  called  the  cells  of  Claudius. 
These  two  varieties  of  cells,  as  well  as  the  epithelial  elements  of  the  sul- 
cus spiralis,  also  contain  a  rigid  fiber,  that  however  is  less  developed 
than  in  the  cells  of  Deiters.  The  centrosomes  of  all  the  epithelial  cells 
of  the  spiral  organ  lie  near  the  free  surface. 


THE    ORGAN    OF    HEARING. 


445 


A  soft,  elastic  cuticular  formation,  the  membra)ia  tectoria,  lies  above 
the  sulcus  spiralis  and  the  spiral  organ  (Fig.  341).  It  is  attached  to  the 
vestibular  lip  of  the  sulcus  and  extends  to  the  outermost  row  of  hair- 
cells. 

The  cochlear  branch  (ramus  cochlearis)  of  the  miditory  nerve  pene- 
trates into  the  axis  of  the  cochlea  and  in  its  spiral  uninterrupted  course 
gives  off  branches  which  pass  toward  the  root  of  the  osseous  spiral 
lamina  ;  here  each  medullated  nerve-fiber  loses  its  medullated  sheath  and 
passes  into  a  nerve-cell,  that  Hke  those  of  the  spinal  ganglia  possesses  a 
connective-tissue  capsule  ;  these  nerve-cells  collectively  form  the  gaji- 
glioii  spiralc,^'  which  winds  around  the  entire  periphery  of  the  axis  of  the 
cochlea  (Fig.  334)  ;  from  the  opposite  pole  of  each  cell  springs  a  second 
nerve-fiber,t  that  soon  acquires  a  medullated  sheath  and  unites  with 
neighboring  fibers  in  a  wide-meshed  plexus  enclosed  in  the  osseous  spiral 
lamina  ;  this  plexus  extends  near  to  the  labium  tympanicum,  where  the 
fibers  lose  their  medullated  sheath,  pass  through  the  foramina  nervina 
(p.  441)  and  end  in  the  epithelium.  This  occurs  in  such  a  manner  that 
they  bend  in  the  direction  of  the  circumvolution  of  the  cochlea  and  run 
in  spiral  cords,  of  which  the  first  passes  to  the  inner  side  of  the  inner 
pillar-cells  (Fig.  339  A),  the  second  into  the  tunnel,  the  third  between 
the  outer  pillar-cells  and  the  first  row  of  the  cells  of  Deiters,  while  the 
remaining  three  run  between  the  cells  of  Deiters.  From  these  cords 
delicate  fibers  proceed  to  the  hair-cells,  on  which  (not  within)  they  ter- 
minate. 

The  arteries  of  the  labyrintJi.  The  auditory  artery  gives  only  a 
small  twig  to  the  membranous  labyrinth  and  another  small  twig  to  the 
osseous  labyrinth  ;  the  majority  of  its  branches  pass  to  the  exit  of  the  fifth, 
seventh,  eighth,  ninth,  and  tenth  cranial  nerves  and  to  the  under  surface 
of  the  cerebellum.  The  artery  for  the  membranous  labyrinth  divides 
into  two  branches  :  i.  The  arteria  vestibularis  (Fig.  342)  sends  twigs  to 
the  vestibular  nerve  and  to  the  lateral-upper  half  of  the  sacculus  and  of 
the  utriculus,  as  well  as  to  the  corresponding  portions  of  the  upper  and 
lateral  semicircular  canals,  which  supply  a  capillary  plexus  that  in  general 
is  wide-meshed,  but  at  the  terminal  points  of  the  vestibular  nerve,  the 
cristae  and  maculae,  is  narrow-meshed.  2.  The  arteria  cochlearis  com- 
munis subdivides  in  two  branches.     The  one  branch,  the  arteria  vestibnlo- 

*  The  ganglion  spirale  possesses  the  same  structure  as  a  spinal  ganglion,  with  a  single 
difference :  the  ganglion  cells  here  are  not  unipolar,  but  bipolar,  as  in  the  embryonal  ganglia 
(p.  113).    The  ganglion  vestibulare  in  the  internal  meatus  also  possesses  bipolar  ganglion  cells. 

f  In  early  developmental  stages  this  fiber  exhibits  the  character  of  a  dendrite  and  only 
gradually  becomes  a  slender  fiber  (^cf.  remark*,  p.  116). 


446 


HISTOLOGY. 


cochlcaris,  supplies  one  twig  to  the  median-posterior  half  of  the  sacculus, 
utriculus,  and  semicircular  canals  and  in  its  minute  ramifications  behaves 
like  the  vestibular  artery  ;  another  twig  ramifies  in  the  initial  third  of  the 
first  turn  of  the  cochlea.  The  other  branch,  the  arteria  cocJilearis  pro- 
pria, supplies  the  remaining  district  of  the  cochlea  ;  on  entering  the  axis 
of  the  cochlea  it  divides   into   three   or   four   branches,  which  in  their 


Arteria  vestibularis. 


a   yrint    .  j^      Arteria  cochlearis  communis 

/ 


Ductus  semicircularis 

superior. 
Ampulla  lateralis. 


Vena  aquseductus 

vestibuli. 
Ductus  semicircularis 
lateralis. 


Arteria  cochlearis 

propria.  ^  Superior 

Arteria  vestibulo-cochlearis. 


Vena  spiralis. 


Vena  vestibularis. 


Ductus  semicircularis 
posterior. 


Arteria  coclilearis  communis. 


Vena  aquaeductus  cochleae. 


Fig.  342. — Scheme.  Blood-vessels  of  the  Right  Human  Labyrinth.  Median  and  Posterior  Aspect. 
B.C.  Ductus  coclilearis.  5.  Sacculus.  V .  Utriculus.  i.  Ductus  reuniens.  2.  Ductus  utriculo-saccularis. 
The  saccus  endolymphaticus  is  cut  off. 

spiral  ascent  form  the  tractus  arteriosus  spiralis.  From  this  about  30  or 
35  radial  twigs  arise,  which  supply  three  separate  capillary  territories: 
(i)  the  canal  in  which  the  ganglion  spirale  is  enclosed,  (2)  the  lamina 
spiralis,    (3)   the   intermediate   and   outer   walls   of  the   scalse  (Fig.  343, 

I.  2,  3)- 

The  veins  of  the  labyrinth  follow  three  separate  paths  : 

I.  The  vena   aqiicediictns  vesiibnli  runs   through    the    aquaeductus 


THE    ORGAN    OF    HEARING. 


447 


vestibuli  ;  it  collects  the  blood  from  the  semicircular  canals  and  from 
one  portion  of  the  utriculus  ;  it  opens  in  the  sinus  petrosus  superior 
(Fig.  342). 

2.  The  vena  aqiiccductns  cocJilar  runs  through  the  aquaeductus 
cochleae  ;  it  collects  the  blood  from  one  portion  of  the  utriculus,  from 
the  sacculus  and  from  the  cochlea.  The  venous  radicles  in  the  cochlea 
behave  in  the  following  manner  :  The  veins  uniting  in  the  vas  proininens 
and  in   the  vas  sph'ale  (Fig.    343,  a,  b)  pass  in   the   wall    of  the  scala 

Scala  tympani.     Scala  vestibuli. 


Stria  vascularis 


Cross-section  of  an  artery  of  the 
tractus  spiralis. 


Vena  lamina  spiralis. 


Ganglion  spirale. 


— -  Vena  spiralis  superior. 


Cross-section  of  an  artery  of  the 
tractus  spiralis. 


- ,  .    ,  ,  ^.  ,  -Vena  lamina  spiralis. 

" — .  Anastomosis. 

" Vena  spiralis  inferior. 

Fig.  343. — Scheme.    Vertical  Section  of  the  Right  Half  of  the  First  (Basal)  and  Second  Turns  of 
THE   Cochlea,     a.  Vas  prominens.     h.  Vas  spirale. 


tympani  to  the  spirally  running  vena  spiralis,  lying  beneath  the  spiral 
ganglion  ;  this  originates  from  the  confluence  of  two  veins,  of  which  the 
lower  receives  the  blood  from  the  first  (basal)  and  a  portion  of  the  second 
turn  of  the  cochlea,  while  the  upper  spiral  vein  collects  the  blood  from 
the  remaining  cochlear  turns.  The  spiral  vein  also  takes  up  one  set  of 
the  capillaries  in  the  canal  of  the  spiral  ganglion  and  is  united  by  anas- 
tomosis with  a  vein  lying  above  this  canal,  the  voia  lamina  spiralis 
(Fig.  343).      This  receives  the  blood  from  the  other  set  of  capillaries  of 


448  HISTOLOGY. 

the  spiral  ganglion,  as  well  as  from  the  lamina  spiralis,*  and  opens  in 
the  central  vein  of  the  cochlea. 

3 .  The  central  vein  of  the  cochlea  is  the  main  radicle  of  the  internal 
auditory  vein.  The  latter  takes  up  veins  from  the  auditory  nerve  and 
from  the  bone,  and  in  all  probability  opens  in  the  vena  spinalis  anterior. 

The  lymph  paths.  The  endolymph  in  the  interior  of  the  mem- 
branous labyrinth  communicates  with  the  subdural  lymph  spaces  b}^ 
means  of  minute  tubules  passing  from  the  saccus  endolymphaticus. 
The  perilymphatic  spaces  {cf.  p.  437)  are  in  connection  with  the  sub- 
arachnoid space  by  means  of  a  lymph-vessel  running  through  the 
aquseductus  cochleae,  the  "  ductus  perilymphaticus."  The  blood-vessels 
and  nerves  are  encircled  by  conspicuous  perivascular  and  perineural 
lymph  spaces,  that  probably  also  are  connected  with  the  subarachnoid 

space. 

The  Middle  Ear. 
The  imicoiis  membrane  of  the  tympanic  cavity  is  intimately  united 
with  the  underlying  periosteum.  It  consists  of  thin  connective  tissue 
and  a  single  stratum  of  cubical  epithelial  cells,  that  sometimes  on  the 
floor,  occasionally  also  in  larger  areas  of  the  tympanic  cavity,  are  ciliated. 
Glands  (short,  o.  i  mm.  long  follicles)  occur  only  and  sparingly  in  the 
anterior  half  of  the  tympanic  cavity.  The  mucosa  of  the  eustachian  tube 
consists  of  a  fibrillar  connective  tissue  (containing  numerous  leucocytes 
near  the  pharyngeal  orifice)  and  of  a  stratified  ciliated  cylinder  epithelium  ; 
the  ciliary  wave  is  directed  toward  the  pharynx.  Mucous  glands  occur  in 
especial  abundance  in  the  pharyngeal  half  of  the  tube.  The  cartilage  of 
the  eustachian  tube,  where  it  adjoins  the  bony  tube,  is  of  the  hyaline 
variety  and  here  and  there  contains  rigid  (not  elastic)  fibers  {cf.  p.  97)  ; 
in  the  anterior  portion  the  matrix  of  the  cartilage  is  penetrated  by  dense 
networks  of  elastic  fibers.  In  the  mucosa  of  the  tympanic  cavity  the 
blood-vessels  form  a  wide-meshed,  in  the  mucosa  of  the  eustachian  tube  a 
narrow-meshed  superficial  capillary  network  and  a  deep  capillary  plexus 
enveloping  the  glands.  The  lymph-vessels  run  in  the  periosteum  of  the 
tympanic  cavity.  With  regard  to  the  terminations  of  the  nerves  exact 
information  is  still  wanting. 

The  External  Ear. 
The   tympanum  consists   of  a  lamina  of  connective  tissue,   lamina 
propria,  in  which  the  fiber-bundles  on  the  surface  facing  lateralward  are 

"  The  vestibular  membrane  is  nonvascular  in  the  adult.  The  arrangement  of  the  blood- 
vessels in  the  cochlea  is  such  that  the  scala  vestibuli  is  chiefly  encircled  by  arteries,  the  scala 
tympani  mainly  by  veins.  The  portion  of  the  scala  tympani  adjacent  to  the  lamina  spiralis 
membranacea  is  thus  removed  from  the  influence  of  arterial  pulsation. 


THE    ORGAN    OF    HEARING. 


449 


radially  arranged  and  connected  with  the  periosteum  of  the  sulcus  tym- 
panicus,  while  on  the  surface  toward  the  tympanic  cavity  the  fiber-bundles 
are  circularly  arranged.  On  its  inner  surface  the  tympanum  is  covered 
by  the  mucous  membrane  of  the  t)'mpanic  cavity,  on  its  outer  surface 
by  the  skin  clothing  the  external  auditory  canal.  Both  coverings  are 
very  firmly  attached  to  the  lamina  propria,  are  smooth,  and  are  without 
papillae.  Where  the  malleus  lies  against  the  tympanum  it  is  provided 
with  a  cover  of  hyaline  cartilage. 

The  external  auditory  meatus,  so  far  as  it  is  cartilaginous  and  on  the 
whole  length  of  its  upper  wall,  is  clothed  with  a  thick  extension  of  the 
skin,  which  is  characterized  by  its  great  abundance  of  peculiar  coil-glands, 


Epidermis. 

Hair-follicle. 
Corium. 

Excretory  duct. 

Young  hair. 
Coil  of  ceruminous  gland. 


Fig.  344. — From  a  Vertical  Section  through 
THE  Skin  of  the  External  Auditory 
Meatus  of  an  Inf.^nt.  X  50.  The  ex- 
cretory duct  opens  into  the  hair-follicle. 
Technic  No.  108. 


Membrana  propria. 

Nuclei  of  smooth  muscle-fibers. 

Secretion. 

Gland-cells. 


B 


Secretion. 


.-  L 


Fig 


, —  Cuticular  border. 
_^_^ ^    M^  Gland-ceOs. 

'>S-P'~C''cv^^^^^-_  Nuclei  of  smooth  muscle- 

*-~i=^=s^—         Membrana  propria. 

345. — A.  Cross-section  of  a  Coil-Tubule  of 
THE  Skin  of  the  External  Auditory  Meatus 
of  an  Infant.  B.  Longitudinal  Section  of  a 
Coil-tubule  from  the  External  Auditory 
Meatus  of  a  Twelve-year-old  Boy.  X  240. 
Technic  No.  igS. 


the  ccniniiiious  glands  (glandulje  ceruminosas).  In  some  respects  these 
glands  correspond  with  the  ordinary  larger  coil-glands  (sweat-glands)  of 
the  skin  ;  like  these  they  possess  an  excretory  duct  clothed  in  several 
layers  of  epithelial  cells,  and  the  canals  of  the  coil  contain  a  simple 
layer  of  usually  cubical  gland-cells,  which  rest  on  smooth  muscle-fibers 
and  a  conspicuous  basement  membrane  (Fig.  344)  ;  they  are  distinguished 
from  the  coil-glands  by  the  very  wide  lumen  of  the  coiled  tubules,  that 
particularly  in  adults  is  greatly  dilated,  and  by  numerous  pigment 
granules  and  fat  droplets  within  the  gland-cells,  which  frequently  exhibit 
a  distinct  cuticular  border.  The  excretory  ducts  are  narrow  and  in  chil- 
dren open  in  the  hair  follicles,  in  adults  close  beside  the  hair-follicles  on 
29 


450 


HISTOLOGY. 


the  free  surface.  The  secretion,  the  cerumen  (ear-wax),  consists  of  pig- 
ment granules,  fat  globules,  and  cells  filled  with  fat ;  the  latter  probably- 
come  from  the  glands  of  the  hair-follicles.  In  the  (remaining)  region 
of  the  bony  external  auditory  meatus  the  skin  is  thin  and  without 
ceruminous  glands. 

The  cartilage  of  the  external  auditory  canal  and  of  the  pinna  is  of 
the  elastic  variety. 

The  vessels  and  nerves  are  distributed  as  elsewhere  in  the  skin  ;  only 
on  the  tympanum  do  they  exhibit  special  peculiarities.  Close  behind  the 
handle  of  the  malleus  an  artery  descends,  which  breaks  up  into  radially 
disposed  branches  ;  the  blood  is  returned  by  two  paths  :  (i)  by  a  venotts 
plexus  extending  along  the  handle  of  the  malleus  and  (2)  by  a  venons 
plexiLS  lying  on  the  margin  of  the  tympanum. 

These  vessels  lie  in  the  external  skin  covering  the  tympanum. 
The  mucous  membrane  covering  the  tympanum  is  also  provided  with  a 
dense  capillary  network,  which  anastomoses  with  the  cutaneous  vascular 
network  by  means  of  perforating  branches  at  the  margin  of  the  tym- 
panum. 

The  lymph-vessels  are  principally  found  in  the  cutaneous  stratum  of 
the  tympanum. 

The  nerves  form  delicate  networks  lying  beneath  the  mucous  and 
cutaneous  covers. 

TECHNIC. 

A  fundamental  condition  is  an  exact  knowledge  of  the  macroscopic 
anatomy  of  the  labyrinth.  The  difficulties,  the  failures,  depend  in  the 
main  on  inaccurate  knowledge  of  the  anatomy  of  the  bony  labyrinth.  As 
a  preliminary  all  parts  lying  lateral  to  the  promontory  (os  tympanicum 
and  ossicles  of  the  ear)  must  be  removed,  so  that  this  is  distinctly  visible. 

^Q  1Q3. — Otoliths. — Chisel  out  the  promontory,  beginning  at  the 
upper  margin  of  the  fenestra  vestibuli,  to  the  lower  margin  of  the  fenestra 
cochleae.  Then,  especially  if  the  bone  is  placed  in  water,  the  white  spots 
(maculae)  in  the  sacculus  and  utriculus  can  be  seen.  With  delicate 
forceps  lift  out  the  saccules  and  spread  a  small  piece  in  diluted  glycerol 
on  a  slide.  The  otoliths  are  present  in  large  numbers,  but  are  very  small, 
so  that  their  shape  can  only  be  distinctly  seen  with  the  high  power  (240 
diameters).  The  glycerol  must  not  be  too  thick,  or  the  otohths  will 
become  completely  invisible  (Fig.  333). 

In  taking  out  the  saccules  portions  of  the  semicircular  canals  are  not 
infrequently  also  removed  ;  stain  these  with  picrocarmine  and  mount 
them  in  dilute  glycerol.  Only  the  epithelium  and  here  and  there  in 
optical  cross-.sections  the  delicate  hyaline  membrane  can  be  seen.  The 
connective  tissue  is  very  scanty. 


THE    ORGAN    OF    HEARING.  45  I 

No.  194. — Surface  preparations  of  the  mcuibraiious  cochlea. — The 
base  of  the  cochlea  lies  in  the  bottom  of  the  internal  auditory  meatus,  the 
apex  is  directed  toward  the  eustachian  tube,  therefore  the  axis  of  the 
cochlea  is  horizontal  and  transverse  to  the  long"  axis  of  the  petrous  bone. 

Chisel  open  the  free  portion  of  the  cochlea,  that  is,  remove  the  prom- 
ontory close  to  the  fenestra  cochleae,  open  the  apex  of  the  cochlea,  and 
having  removed  the  superfluous  osseous  mass  as  far  as  practicable  place 
the  preparation  in  20  c.c.  of  0.5  per  cent,  osmic  acid  (5  c.c.  of  2  per  cent, 
osmic  acid  to  15  c.c.  of  distilled  water).  In  from  twelve  to  twenty  hours 
wash  the  preparation  for  about  one  hour  and  then  place  it  in  200  c.c.  of 
Mi^iller's  fluid.  In  from  three  to  twenty  days  (or  later)  open  the  cochlea 
fully  and  examine  it  under  water.  The  osseous  spiral  lamina  can  be  seen  as 
a  delicate  lamella,  the  membranous  spiral  lamina  as  a  delicate  membrane, 
attached  to  the  axis  of  the  cochlea  ;  with  fine  forceps  break  off  a  little 
piece  of  the  osseous  spiral  lamina  ;  do  not  lift  it  with  the  forceps,  but  care- 
fully with  needle  and  section-lifter  remove  it  from  the  fluid  and  transfer  it 
to  a  drop  of  dilute  glycerol  on  a  slide.  It  is  advisable  to  break  off  the  axial 
portion  of  the  bony  spiral  lamina  on  the  slide  with  needles,  because  the 
relatively  thick  osseous  process  renders  it  difficult  to  apply  a  cover-glass. 
The  vestibular  surface  of  the  lamina  must  be  directed  upward  ;  it  can  be 
recognized  by  the  auditory  teeth,  which  are  visible  when  the  upper  sur- 
face is  in  focus  (Fig.  336),  while  the  other  portions  are  not  distinct  until 
the  tube  is  depressed  and  the  lower  planes  are  focused.  With  the  low- 
power  only  the  interstices  of  the  auditory  teeth  are  at  first  visible  as  dark 
streaks  (Fig.  338,  labium  vestibulare) ;  the  papillae  likewise  cannot  be 
seen  immediately,  even  with  the  high  power,  but  become  distinct  after 
the  second  or  third  day.  The  chief  difficulty  lies  not  in  the  finishing, 
but  in  the  proper  examination  of  the  object ;  the  picture  alters  with  the 
slightest  change  in  focus.  In  Fig.  339  B  the  membranous  spiral 
lamina  is  drawn  schematically,  as  seen  with  the  upper  surface  in  focus, 
therefore  only  the  free  surface  of  the  structure,  drawn  as  seen  from  the 
side  in  A,  is  visible.  It  is  clear  that  in  lowering  the  tube  the  head- 
plates  of  the  pillar-cells  are  no  longer  visible,  but  their  bodies  (as  circles 
in  optical  cross-section)  ;  the  reticular  membrane  likewise  disappears,  it 
can  be  seen  only  when  the  surface  is  in  focus.  The  preparation  may 
be  stained  with  picrocarmine  and  preserved  in  dilute  glycerol.  The  fore- 
going directions  are  intended  to  apply  to  the  human  ear  and  that  of  the 
cat.     The  labyrinths  of  children  are  recommended. 

No.  195. — Sections  of  the  bony  and  vicnibranons  cochlea. — Remove 
the  cochlea  of  a  child  *  from  the  labyrinth.  The  compact  osseous  sub- 
stance of  the  cochlea  is  surrounded  by  spongy  bone  so  soft  that  it  can 
be  removed  with  a  stout  penknife.  Having  done  this,  with  a  chisel 
make  small  openings  in  the  cochlea  at  two  or  three  places,  about  i  mm. 
square,  in  order  to  facilitate  the  penetration  of  the  fixation  fluid.      Then 

*  Among  animals  the  cochlea  of  the  guinea-pig  or  the  bat  is  recommended  ;  it  is  not 
embedded  in  spongy  bone  and  without  further  chiseling  and  puncturing  can  at  once  be  placed 
in  the  fixing  fluid.      The  cochlea  of  kittens  is  also  recommended. 


452  HISTOLOGY. 

place  the  cochlea  in  30  c.c.  of  Hermann's  solution  (p.  22).  After  48 
hours  remove  the  object,  wash  it  for  a  few  seconds  in  methyl  alcohol, 
transfer  it  to  crude  pyroligneous  acid  for  from  12  to  24  hours,  and  then 
harden  it  in  about  60  c.c.  of  gradually  strengthened  alcohols  (p.  35). 
When  the  hardening  is  completed  the  cochlea  is  decalcified  in  concen- 
trated aqueous  (or  better  alcoholic)  solution  of  picric  acid.  When  the 
object  is  decalcified  harden  it  again,  first  in  50  per  cent.,  then  in  70  per 
cent,  alcohol,  and  after  about  a  week  embed  it  in  liver  or  in  celloidin  and 
cut  sections  parallel  with  the  long  axis  of  the  cochlea.  Mount  them  in 
xylol-balsam. 

It  is  not  very  difficult  to  obtain  preparations  affording  a  general  view. 
The  ^■e5tibular  membrane  is  often  torn,  so  that  the  ductus  cochlearis  and 
scala  vestibuli  appear  as  a  common  space.  The  spiral  organ  leaves  most 
to  be  desired  ;  only  very  thin  sections  which  pass  through  the  organ  ver- 
tically furnish  wholly  intelligible  pictures  ;  usually  a  section  contains  sev- 
eral inner  and  outer  pillar-cells,  in  part  only  fragments  of  them  ;  the  cells 
of  Hensen  appear  puffed  and  swollen  (Fig.  341),  so  that  orientation  pre- 
sents many  difficulties  to  the  beginner. 

No.  196. —  Tlie  nerves  of  the  niaciilcE,  cristce,  and  cocJilea. — For  this 
purpose  the  ear  of  the  newborn,  up  to  ten-day-old  mouse  is  recom- 
mended, treated  according  to  the  method  given  on  page  45,  No.  17.  The 
base  of  the  cranium,  after  removal  of  the  vertex,  brain,  and  lower  jaw,  is 
placed  for  from  three  to  four  days  in  the  osmio-bichromate  mixture  and 
for  two  days  in  the  silver  solution.  As  a  rule  it  is  necessary  to  employ 
the  "double"  method  (p.  47J.  Cut  horizontal  and  frontal  sections 
through  the  undecalcified  cranium.  The  former  are  the  more  readily 
made. 

No.  197. —  The  eiistachia7i  tube. — To  obtain  transverse  sections  (in- 
cluding cartilage  and  mucosa)  the  oblique  direction  of  the  tube  downward, 
forward,  and  inward  must  be  ascertained.  Cut  out  the  entire  pharyngeal 
division  of  the  tube  together  with  the  surrounding  muscles  and  fix  it  in 
200  or  300  c.c.  of  Miiller's  fluid  (p.  33).  In  from  three  to  six  weeks 
wash  it  in  running  water  and  harden  it  in  .100  c.c.  of  gradually  strength- 
ened alcohols  (p.  35).  The  sections  ma}'  be  stained  in  Hansen's  hema- 
toxylin (p.  38)  and  mounted  in  xylol-balsam.  For  a  general  view 
examine  with  the  low  power. 

No.  198. — The  cernniinotis  glands. — Cut  off  the  ear  and  the  carti- 
laginous auditory  meatus  close  to  the  bony  auditory  meatus.  From  the 
cartilaginous  portion  cut  a  piece  i  cm.  square  and  place  it  in  30  c.c.  of 
absolute  alcohol.  The  tissue  may  be  sectioned  on  the  following  day. 
If  it  is  desired  to  see  the  coil  and  the  excretor}'  duct  the  sections  must 
be  tolerably  thick  ( — 0.5  mm.)  (Fig.  344).  Nuclear  staining  with 
Hansen's  hematoxylin  (p.  38)  may  be  employed.  Examine  thin  un- 
stained sections  in  diluted  glycerol  ;  in  these  the  fat-  and  the  pigment- 
granules  can  be  seen.  The  organs  of  infants  are  especially  recommended 
for  these  preparations.      In  adults  the  tubules  are  widely  dilated  and  do 


THE    OLFACTORY    ORGAN.  453 

not  furnish  satisfactory  general  views.  On  the  other  hand,  the  cuticular 
border  of  the  gland-cells  is  distinct  in  older  children  and  in  adults,  which 
in  the  newborn  I  miss  (cf.  Fig.  345). 


XII.   THE   OLFACTORY   ORGAN. 

In  this  chapter  the  structure  of  the  entire  nasal  mucous  membrane 
will  be  described.  The  olfactory  mucous  membrane  proper  in  man  is 
confined  to  the  middle  of  the  superior  turbinal  bone  and  to  the  cor- 
responding portion  of  the  nasal  septum  ;  the  remaining  portions  of  the 
nasal  fossae  (the  accessory  nasal  spaces  included)  are  covered  with  res- 
piratory mucous  membrane.  In  addition  there  is  another  division  in  the 
region  of  the  movable  nose  (vestibulum  nasi)  which  is  clothed  by  a  con- 
tinuation of  the  external  skin.*  Accordingly  three  divisions  of  the  nasal 
mucous  membrane  differing  in  structure  are  to  be  distinguished. 

The  Vestibular  Region. 
The  mucous  membrane  of  the  vestibular  region  consists  of  a  strati- 
fied squamous  epithelium  and  a  tunica  propria    supporting    papillae,    in 
which  numerous  sebaceous  glands  and  the  hair-follicles  of  the  stiff  nasal 
hairs  (vibrissae)  are  embedded. 

The  Respiratory  Region. 

The  respirator)-  division  of  the  nasal  mucous  membrane  consists  of 
a  many-rowed  ciliated  c\-linder  epithelium  (Fig.  20),  that  sometimes 
contains  many,  sometimes  few  goblet-cells,  and  of  a  conspicuous  tunica 
propria,  on  the  inferior  turbinal  bone  up  to  four  millimeters  thick,  which 
is  built  of  fibrillar  connective  tissue  and  of  a  large,  variable  number  of 
leucocytes,  and  toward  the  epithelial  border  is  condensed  to  a  homo- 
geneous membrana  propria  provided  with  minute  perforations.  These 
leucocytes  are  occasional!}-  balled  together  in  solitary  nodules  and  often 
wander  in  large  numbers  through  the  epithelium  into  the  nasal  fossse 
{cf.  p.  260). 

The  tunica  propria  in  man  contains  branched  alveolo-tubular  mixed 
glands  {cf.  p.  242)  ;  the  serous  divisions  are  provided  with  intercellular 
secretory  capillaries,  serous  and  mucous  gland-cells  with  a  trophospon- 
gium  (p.  64).  Not  infrequently  they  open  in  funnel-shaped  depressions, 
which  are  lined  by  an  extension  of  the  surface  epithelium  and  on  the  in- 

*  The  boundaries  are  very  variable  ;  stratified  squamous  epithelium  is  frequently  found  on 
the  middle,  less  often  on  the  inferior  turbinal. 


454  HISTOLOGY. 

ferior  turbinal  are  perceptible  to  the  unaided  eye.      In  the  accessory  nasal 
spaces  the  epithelium  and  tunica  propria  are  considerably  thinner  ( — 0.02 


Tunica 
propria. 


'""  Vein. 


■■^^SSS^S?^''    ?'":;3£^|P-^'^*"'^"- 


■  '  .•^•:.:!^t<•,^■V^•:••■■/■-^^•V^v^^•■;■■.T■.:^^-■y•^•te■•••■■  .  -.  .  ■  .     .      • 


Mucous 
gland-cells. 


Serous  cells. 


»■  .       -  •    -      ..  .  ..>"'- «r,.  ■■ 


— ■   Artery. 


Fig.  346. — Vertical  Section  through  the  Mucosa  of  the  inferior  Turbinal  of  Man.  X'48.  On 
the  left  is  a  funnel-shaped  depression  taking  up  a  portion  of  an  e.xcretory  duct  ;  nearby  on  the  right  is  the 
section  of  a  large  vein.     Technic  No.  200. 

mm.),  but  otherwise   of  the  same   structure  ;  the   glands   are   small  and 
few  in  number. 

The  Olfactory  Region. 

The  mucous  membrane  of  this  region  by  its  yellowish-brown  color 
can  be  macroscopically  distinguished  from  the  rosy  mucosa  of  the  res- 
piratory division.  It  consists  of  an  epithelium,  the  olfactory  epithelium, 
and  of  a  tunica  propria.  In  the  olfactory  epithelium  two  forms  of  cells 
occur.  The  one  form  (Fig.  347,  si)  is  cylindrical  in  its  upper  half  and 
here  contains  a  yellowish  pigment  and  minute   granules,  often  arranged 


THE    OLFACTORY    ORGAN.  455 

in  longitudinal  rows.  The  lower  half  is  slenderer,  the  edges  are  serrated 
and  invaginated,  the  inferior  end  is  forked  and  is  said  to  unite  with  the 
forked  ends  of  neighboring  cells  in  a  protoplasmic  network.  These  ele- 
ments are  called  supporting  cells.  Their  usually  oval  nuclei  lie  at  the 
same  level  and  in  vertical  sections  occupy  a  narrow  belt,  the  zone  of  the 
oval  nuclei  (Fig.  350).  The  second  form  (Fig.  347,  r,  and  Fig.  348) 
possesses  a  usually  spherical  nucleus  and  only  in  the  vicinity  of  the  latter 
an  appreciable  amount  of  protoplasm  ;  from  this  a  slender  cylindrical 
process,  bearing  minute  hairs,  extends  upward,  while  below  from  the 
opposite  side  a  very  delicate  process  continues  directly  into  the  axis- 
cylinder  of  a  nerve-fiber.  These  cells,  the  olfactory  cells,  are  ganglion 
cells  and  their  lower  process  is  a  centripetal  nerve-fiber.  Their  round 
nucleolated  nuclei  lie  at  different  levels  and  occupy  a  broad  belt,  the  zone 
of  tJie  round  nuclei  {¥\g.  350,.:^;').*  In  addition  to  these  two  forms  of 
cells  there  are  intermediate  forms,  that 
sometimes  resemble  the  olfactory  ele- 
ments, sometimes  the  supporting  cells.  \  ~  ^ 
At  the  border  of  the  epithelium,  toward 

the  connective  tissue,   there  is  a  proto-  ,    ,        ,  ,  ,,  ^.-       .    ^^ 

plasmic  network  furnished   with   nuclei,  \\f»^     E^.v^     .--:r'A* 

the  so-called  basal  cells  (Fig.  350,  b). 
The  surface  of  the  epithelium  is  covered 
with  an  extremely  delicate,  homogeneous 
membrane,  the  mcvibrana  limitans  olfac-     ^'°Toty  MpcosI^Ff  r^L"/.  Tsto"^^ 

,       •  •■    •        •  1  L      ^1        i<     •!•    i.    J  >>         J  Supporting    cells;    j.  extruded  mucus  re- 

toria  ;  it  is  pierced  by  the        ciliated       ends  semblmg  cilia;  r,  olfactory  cells,  at/'  the 

i-    .  ,  f.  ,,  ,..,_  ,  lower  process  has  been  torn  off;  /,  ciliated 

01  the  olfactory  cells  and  is  itSelt  covered  ceU;  6,  cells  of  olfactory  glands.     Technic 

Xo.  199. 

with  a  peculiar  mass,  regarded  by  some 

authors  as  a  cuticulaf  formation  similar  to  that  of  the  intestinal  epi- 
thelium, by  others  as  delicate  cilia,  by  still  others  interpreted  as  minute 
drops  of  discharged  mucus  (Fig.  337,  s). 

The  tunica  propria  consists  of  a  loose  feltwork  woven  of  rigid  con- 
nective-tissue fibers,  intermingled  with  delicate  elastic  fibers,  which  in 
some  animals  (for  example,  in  the  cat)  toward  the  epithelium  is  con- 
densed to  a  structureless  membrane.  Numerous  glands,  the  olfactory 
glands  (glandule  olfactorije,  Bowman),  are  embedded  in  the  tunica 
propria  ;  they  are  either  simple  or  (for  example,  in  man)  branched  folli- 
cles, in  which  an  excretory  duct  {a)  situated  in  the  epithelium,  a  body  (/'), 


*  Occasionally  in  the  non-nucleated  epithelial  territory  round  nuclei,  varying  in  quan- 
tity, are  found  above  the  zone  of  oval  nuclei  ;  they  either  belong  to  dislocated  olfactory  cells 
(^Fig.  350)  or  are  the  nuclei  of  wandering,  often  pigmented  leucocytes. 


456 


HISTOLOGY. 


and  a  fundus  (g)  can  be  distinguished  *  (Fig.  349).  The  cells  of  the 
body  of  the  glands  are  pigmented.  The  olfactory  glands  (also  those  of 
man)  until  recently  were  regarded  as  serous  glands  ;  latterly  they  have 
been  interpreted  as  mucous  glands.      The  tunica  propria  also  carries  the 


Epithelium. 


Tunica  propria. 


Fiber-bundle  of  the  olfactory  nerve.  Centripetal  process  of  an  olfactory  cell. 

Fig.  348. — \'ertical  Section  through  the  Olfactory  Region  or  a  Young  Rat.     X  4S0.     Technic  No.  202. 

ramifications  of  the  nerves.  The  branches  of  the  olfactory  nerve  are 
enveloped  in  processes  of  the  dura  and  consist  exclusively  of  nonmedul- 
lated  fibers,  that  readily  separate  into  their  component  fibrillae  ;  the 
fibers  are  the  inferior  processes  of  the  olfactory  cells  united  in  bundles, 


^  I  Epithelium. 


Tunica  propria. 


6 — 


..-J 


Fig.  349. — Vertical  Section  of  the  Olfactory  ^Mucosa  of  a  Rabbit.  X  50.  zo.  Zone  of  oval,  zr,  zone  of 
round  nuclei,  dr.  Olfactory  glands;  a,  excretory  duct,  k,  body,  g,  fundus,  n,  Branches  of  olfactory  nerve 
cut  transversely,    v,  Vein;  ar,  arterj-.    b.  Bundles  of  connective  tissue  in  cross-section.     Technic  No.  201. 

which  pass  in  shallow  curves  from  the  epithelium  and  descend  into  the 
tunica  propria  and  by  union  with  neighboring  bundles  form  the  branches 
of  the  olfactory  nerve.     The  terminal  ramifications  of  the  fifth  nerve  lie 


*The  olfactory  glands  frequently  overstep  the  territory  of  the  olfactory  mucous  membrane 
and  are  found  in  the  adjoining  divisions  of  the  respiratory  mucous  membrane. 


THE    OLFACTORY    ORGAN. 


457 


within  the  tunica  propria  ;  deHcate  fibers  that  ascend  into  the  epitheUum 
and  there  terminate  in  free  ends  possibh-  belong  to  the  fifth  nerve.* 

Of  the  blood-vessels  of  the  nasal  mucosa  the  arterial  stems  run  in  the 
deeper  strata  of  the  tunica  propria  (Fig.  346,  Fig.  349)  ;  they  supply  a 
capillary  network  that  reaches  close  beneath  the  epithelium.  The  veins 
are  remarkable  for  their  conspicuous  development  (Fig.  346) ;  over  the 
posterior  end  of  the  inferior  turbinal  they  form  so  dense  a  network  that 
the  tunica  propria  resembles  cavernous  tissue. 

The  hnnpJi-vessels  form  coarse-meshed  nets  lying  in  the  deeper  strata 
of  the  tunica  propria.  The  lymph-vessels  of  the  olfactory  mucosa  can 
be  injected  from  the  subarachnoid  space,  through  the  perineural  sheaths 


prfT'n  p  ^TTTf^^ 


xr{ 


\    h 


Tunica  propria. 


dr — 


■-^i^^ 


^S 


m 


Fig.  350. — Vertical  Section  through  the  OLrACTORV  Mucosa  of  a  Rabbit.  X  560.  .j,  Cuticular  border; 
20,  zone  of  oval,  zr,  zone  of  round  nuclei;  b,  basal  cells;  dr.  portions  of  olfactory  glands,  on  the  right  the  lower 
portion  of  the  e.xcretory  duct  is  shown;  n.  branch  of  the  olfactory  nerve.     Technic  Xo.  202. 

of  the  branches  of  the  olfactory  nerve  obtained  from  the  cerebral  mem- 
branes on  passing  through  the  cribriform  plate. 

Medullated  twigs  of  the  fifth  nerve  can  be  found  in  the   respiratory 
as  well  as  in  the  olfactory  mucosa. 


TECHNIC. 

^o.  199. — Olfactory  cells. — Saw  open  in  the  median  line  the  head 
of  a  rabbit  just  killed.      The  olfactory  mucosa  is  easily  recognized  by  its 

*  Difterent  authors  have  described  structures  in  the  nasal  mucous  membrane  resembling 
the  taste-buds.  However,  it  is  not  certain  but  that  folds  of  the  nasal  mucous  membrane  may 
have  been  mistaken  for  these  "  olfactory  buds." 


45  8  HISTOLOGY. 

brown  color.  With  fine  scissors  carefully  cut  out  a  piece  of  the  mucosa, 
about  5  mm.  square,  together  with  the  corresponding  portion  of  the 
turbinal  bone,  and  place  it  in  20  c.c.  of  one-third  alcohol  (p.  20).  In 
from  five  to  seven  hours  transfer  the  same  to  5  c.c.  of  picrocarmine  and 
on  the  following  day  to  10  c.c.  of  distilled  water.  In  about  ten  minutes 
remove  the  piece  and  lightly  toss  it  against  a  slide  on  which  a  drop  of 
diluted  glycerol  has  been  placed  ;  stirring  with  the  needle  is  to  be 
avoided.  Carefully  apply  a  cover-glass.  In  addition  to  many  fragments 
of  cells  many  well-preserved  supporting  elements  will  be  seen.  Very 
frequently  the  exceedingly  delicate  central  process  of  the  olfactory  cells 
is  wanting  (Fig.  347). 

No.  200. —  TJie  mucous  membrajie  of  the  respiratory  region. — Incise  a 
piece  of  the  mucosa  about  5  or  10  mm.  square  on  the  lower  half  of  the 
nasal  septum  ;  strip  it  off  and  fix  and  harden  it  in  about  20  c.c.  of 
absolute  alcohol  (p.  20).  Use  the  nasal  mucous  membrane  of  the  rab- 
bit's head  (No.  199)  for  thin  sections  ;  embed  the  pieces  in  liver  and  stain 
the  sections  with  Hansen's  hematoxylin  ;  mount  in  xylol-balsam.  For 
general  views  the  mucous  membrane  of  human  cadavers  answers,  which 
is  to  be  treated  in  the  same  manner,  except  that  thick,  unstained  sections 
are  to  be  mounted  in  diluted  glycerol. 

No.  201. —  TJie  mucous  membrane  of  the  olfactory  region. — Remove 
pieces  from  3  to  6  mm.  square  of  the  brown  mucosa  from  the  upper 
portion  of  the  nasal  septum  of  a  rabbit  (No.  199),  and  place  them  for 
three  hours  in  20  c.c.  of  Ranvier's  alcohol,  which  somewhat  loosens  the 
elements  of  the  olfactory  epithelium.  Transfer  the  pieces  carefully  to 
3  c.c.  of  2  per  cent,  osmium  solution  plus  3  c.c.  of  distilled  water,  and 
place  the  whole  for  from  fifteen  to  twenty-four  hours  in  the  dark.  At 
the  expiration  of  this  time  the  pieces  are  to  be  placed  for  a  half-hour  in 
20  c.c.  of  distilled  water  and  then  hardened  in  30  c.c.  of  gradually 
strengthened  alcohols.  The  hardened  pieces  are  to  be  embedded  in 
liver  and  sectioned  ;  the  sections  are  to  be  stained  from  twenty  to  thirty 
seconds  in  Hansen's  hematoxylin  and  mounted  in  xylol-balsam. 

In  order  to  obtain  good  views  of  the  glands  make  thick  sections 
transverse  to  the  course  of  the  nerve-fibers  (Fig.  349).  For  the  exhibi- 
tion of  the  nerve-fibers  and  the  epithelium  thin  sections  parallel  to  the 
course  of  the  fibers  are  suitable  (Fig.  350). 

No.  202. — The  nerve-processes  of  the  olfactory  cells  may  be  obtained 
in  preparations  made  according  to  No.  196,  p.  452.  Often  the  duct 
system  of  the  olfactory  glands  is  blackened. 


XIII.   THE   GUSTATORY   ORGAN. 

The  gustatory  organ,  the  taste-buds,  are  usually  ellipsoidal  bodies, 
about  80  fj.  long  and  40  /y.  broad,  occasionally  they  are  more  nearly  spheri- 
cal, which  are  completely  embedded  in  the  epithelium  of  the  oral  mucous 


THE    GUSTATORY    ORGAN. 


459 


membrane  ;  their  base  rests  upon  the  tunica  propria,  their  upper  end 
reaches  near  to  the  surface  of  the  epitheHum,  which  here  exhibits  a  small, 
often  funnel-shaped  depression,  the  taste-canal ^  the  outer  end  of  which 
is  named  the  outer  taste-pore,  the  inner  end  the  inner  taste-pore.  Each 
taste-bud  consists  of  two  kinds  of  slender  epithelial  cells  ;  the  one  either 


•^^ 


"■'  "■^'"'^    I?' 


,'M^^^'fV^  mum 


Epithelium. 


Tunica  propria. 


Fig.  351. — Vertical  Section  of  two  ridges  of  the  Papilla  Foliata  of  a  Rabbit.  X  80.  Each  ridge,  I, 
bears  three  secondary  ridges,  /';  g,  taste-buds;  n,  medullated  nerves;  d,  serous  gland;  a,  portion  of  an  ex- 
cretory duct  of  a  serous  gland;  M,  muscle-fibers  of  the  tongue.     Technic  No.  204. 

are  everywhere  of  the  same  diameter  or  taper  at  the  basal  end,  which 
occasionally  is  forked,  while  the  upper  end  is  prolonged  to  a  fine  point ; 
their  protoplasm  is  clear.  These  cells  constitute  the  bulk  of  the  taste- 
bud,  are  principally  situated  at  the  periphery  of  the  bud,  and  are  called 
tegine)ital  cells  (covtr-coWs).      They  serve  as   support  and  sheath  for  the 


Gustatory  canal. 
Gustatory  process. 


Taste-bud. 


k. 


Epithelium. 


Tunica  propria. 


Fig.  352. — From  a  Vertical  Section  of  the  Papilla  Foli.ata  of  a  Pi.\BBiT.      X  560.     Technic  No.  204. 

gustatory  cells  (taste-cells),  which  are  the  real  sensory  epithelial  element.-". 
The  gustatory  cells  are  small  and  only  slightly  thickened  where  the 
nucleus  is  situated,  which  is  sometimes  nearer  the  lower  end,  some- 
times in  the  middle,  rarely  at  the  upper  end  of  the  cell.  The  upper 
division  of  the  cell  is  cylindrical  or — more  frequently — conical,  and  bears 


460 


HISTOLOGY. 


on  its  free  end  a  refractile  process,  a  cuticular  formation,  that  reaches 
to  the  inner  taste-pore  (Fig.  352);  the  lower  division  is  sometimes 
slender,  sometimes  thick,  and  terminates  in  a  blunted  end  or  in  a  tri- 
angular foot,  without  however  extending  into  the  connective  tissue  of 
the  mucosa.     Their  protoplasm  is  granular. 

The  taste-buds  chiefly  occur  in  the  lateral  walls  of  the  vallate 
papiHse  [cf.  Fig.  185,  p.  258)  and  on  the  ridges  of  the  foliate  papillae 
(Fi&-  SSOj  (^-  P-  259),  hi  lesser  number  on  the  anterior  and  posterior- 


Taste-bud. 


Intergemmal  fibers. 


ft:    ^  ^^''•"    ^ 


Secondary  ridge. 
Epithelium. 


Intragemmal  fibers. 


Secondary  ridge. 


Connective  tissue. 


Fig.  353. — From  a  Vertical  Section  of  the  Foliate  Papilla  of  a  Rabbit.     X  220.  _  At  x  the  intergemmal 
fibers  lie  upon  a  taste-bud.     For  orientation  compare  with  Fig.  351.     Technic  No.  205. 

lateral  fungiform  papillae  and  on  the  posterior  surface  of  the  epiglottis. 
In  the  human  fetus  of  from  5  to  7  months  they  are  more  numerous  * 
than  in  the  adult. 

The  conjecture  that  the  terminal  ramifications  of  the  glossopharyn- 
geal nerve  have  the  same  anatomic  relation  to  the  gustatory  cells  that 
the  olfactory  nerve-fibers  have  to  the  olfactory  cells  has  been  shown  to 
be  erroneous.      The  terminal  branches  of  the  glossopharyngeal  nerve 


*  They  are  found  on  many  filiform  papillae,  as  well  as  on  the  vallate  papillae.  Later  they 
atrophy  and  their  remains  are  taken  away  by  leucocytes  that  have  wandered  in.  Not  infre- 
quently in  adults  leucocytes — often  in  large  quantities — are  found  in  the  interior  of  the  taste- 
buds. 


THE    GUSTATORY    ORGAN.  461 

consist  of  medullated  and  nonmedullated  ner\'e-fibers  beset  with  micro- 
scopic (sympathetic)  ganglia,*  which  form  a  dense  plexus  in  the  tunica 
propria,  from  which  numerous  branches  arise.  Some  of  the  latter,  per- 
haps, terminate  in  the  connective  tissue  in  end-bulbs,  but  the  majority  of 
the  (nonmedullated)  fibers  penetrate  into  the  epithelium.  Here  two 
kinds  of  fibers  can  be  distinguished.  The  one  kind,  the  "  intragemmal  "  f 
fibers,  enter  the  taste-buds  (Fig.  353),  divide  and  form  a  plexus  beset 
with  numerous  conspicuous  varicosities,  that  extends  up  to  the  taste- 
pore  ;  the  intragemmal  ramifications  of  the  nerve-fibers  do  not  anasto- 
mose with  one  another,  nor  do  they  unite  with  the  gustatory  cells,  but 
all  terminate  in  free  ends.  The  other  kind,  the  smoother  "  intergem- 
mal  "  fibers,  penetrate  the  epithelial  areas  between  the  taste -buds  and 
without  dividing  usually  extend  into  the  uppermost  strata  of  the  epithe- 
lium. 

TECHNIC. 

No.  203. — For  orientation  regarding  the  nnviber  and  position  of  the 
taste-buds  proceed  according  to  the  method  in  No.  102  (p.  298).  Suita- 
ble objects  are  the  vallate  papillae  of  any  animal  {cf.  Fig.  185)  and  the 
papillae  foliatae  of  the  rabbit.  The  latter  consist  of  elevated  groups  of 
parallel  folds  of  the  mucosa,  situated  one  on  either  edge  of  the  root  of 
the  tongue.  In  moderately  thin  sections  vertical  to  the  long  axis  of 
the  folds  the  taste-buds  can  be  recognized  with  the  low  power  as  clear 
spots. 

No.  204. —  Tlie  minute  structure  of  the  taste-buds. — Dissect  off  with 
straight  scissors  a  papilla  foliata  of  a  rabbit  just  killed,  with  as  little  as 
possible  of  the  subjacent  muscle  substance.  Pin  the  papilla  with  spines 
on  a  cork  stopper,  the  muscle  side  toward  the  cork,  and  expose  it  for  one 
hour  to  the  vapor  of  osmic  acid  (see  further  p.  34,  No.  10).  Thin  sections 
of  the  hardened  preparation  embedded  in  liver  are  to  be  stained  thirty 
seconds  in  Hansen's  hematoxylin  (p.  38)  and  mounted  in  xylol-balsam 
(Fig.  35  0- 

No,  205. — Exhibition  of  the  nerves. — Place  the  papillae  foliatae  of  a 
rabbit  for  three  days  in  the  osmio-bichromate  mixture,  for  two  days  in 
the  silv^er  solution  (p.  45).  The  "  double  "  method  is  recommended.  The 
intergemmal  fibers  are  more  numerous  and  more  readily  blackened  than 
the  intragemmal  fibers,  which  are  exceedingly  delicate  (Fig.  353).  Fre- 
quently single  tegmental  and  gustatory  cells  become  blackened. 

*  Whether  the  so-called  "  taste  granules  "  beneath  the  epithelium  of  the  papillae  foliatae 
are  multipolar  nerve-cells  is  very  questionable  ;   a  nerve-process  has  not  yet  been  demonstrated. 
f  From  gemma,  the  bud. 


APPENDIX. 


MICROTOME    TECHNIC. 
The    Microtome. 

The  commonh'  used  microtomes  are  constructed  according  to  two 
different  principles. 

The  principle  of  the  one  kind  consists  therein,  that  the  object  to  be 
sectioned  is  elevated  by  the  shifting  of  the  object-holder  up  an  inclined 
plane. 

In  the  other  form  the  object  is  deviated  in  a  vertical  direction  by  a 
micrometer-screw. 

Both  kinds  are  excellent  instruments.* 

All  parts  of  the  microtome  should  be  kept  as  clean  as  possible. 
When  not  in  use  it  should  be  protected  from  dust  by  covering  it  with  a 
light  wooden  case.  The  slideway  in  which  the  knife  moves  must  be  kept 
scrupulously  clean.  It  should  be  occasional!}'  cleansed  with  a  cloth 
moistened  in  benzin  and  then  should  be  freely  lubricated  with  vaselin,  so 
that  the  sliding-block  will  pass  evenly  throughout  the  entire  slideway  at 
the  lightest  touch. t  Especial  care  must  be  bestowed  upon  the  knife. 
Only  with  a  very  sharp  knife  can   series   of  very  thin   sections  be  made. 

*The  workmanship  of  the  sliding  microtomes  of  Thoma,  made  by  Jung  in  Heidelberg,  is 
excellent,  as  I  know  from  my  own  experience.  The  size  No.  IV  is  especially  recommended. 
The  microtomes  constructed  on  the  same  principle  by  G.  Miehe,  in  Hildesheim,  are  also  highly 
recommended. 

t  The  slideway  of  the  Thoma  microtome  should  be  less  freely  oiled,  to  prevent  the  object- 
holder  from  recoiling  backward. 

Editor' s  remark  :  The  automatic  microtome  of  Minot  is  widely  used,  particularly  in 
American  laboratories.  This  instrument  is  distinguished  from  those  above  described  by  the 
great  rapidity  with  which  it  can  be  worked.  Therefore  it  is  to  be  highly  recommended,  espe- 
cially for  the  preparation  of  long  series  of  paraffin  sections  attached  one  to  the  other  in  the  form 
of  a  ribbon  ("  ribbon-cutting").  In  exactness  of  action  it  is  hardly  surpassed  by  the  German 
models,  from  which  it  altogether  differs  in  construction.  The  object  is  moved  by  the  rotation  of 
a  wheel  in  a  vertical  direction  up  and  down  across  the  edge  of  a  knife  and  previous  to  everv 
cut  is  advanced  toward  the  knife  a  certain  distance,  which  is  regulated  by  an  automatic  microm- 
eter-screw. 

It  is  difficult  to  recommend  in  particular  any  of  the  microtomes  mentioned.  Each  has  its 
advantages  and  disadvantages,  and  to  be  successfully  used  demands  a  certain  amount  of  ex- 
perience and  practice,  which  determines  the  individual  preference  for  a  certain  instrument. 

The  Minot  microtome  is  made  by  E.  Zimmermann,  Leipzig,  Germany,  and  in  the  United 
States  by  the  Bausch  &  Lomb  Optical  Co.,  New  York.  The  latter  also  make  a  very  satisfac- 
tory sliding  microtome,  on  the  principle  of  the  Schanze  microtome. 


464  HISTOLOGY. 

A  really  sharp  knife  should  easily  cut  a  thin    hair  held  at    one    end 
between  the  fingers. 

Embedding. 
the  paraffin  method. 

The  following  materials  and  apparatus  are  required  : — 

1.  Paraffin:  two  kinds,  a  soft  (melting-point  45°  Celsius)  and  a 
hard  (melting-point  52°  Celsius).  Of  this  prepare  a  mixture  which 
melts  at  50°  Celsius.  Much  depends  on  the  proper  proportions  of  the 
two  sorts  of  paraffin  in  the  mixture  ;  many  a  failure  is  due  to  an  unsatis- 
factory mixture.  The  precise  proportions  cannot  be  given,  because  the 
consistence  of  the  paraffin  depends  in  a  great  measure  on  the  outer  tem- 
perature. Hard  objects,  as  well  as  the  cutting  of  very  thin  sections, 
require  a  harder  mixture  than  usual.  For  winter,  at  a  room-tempera- 
ture of  20°  Celsius,  a  mixture  of  30  grams  of  soft  and  25  grams  of  hard 
paraffin*  answers  for  most  purposes. 

2.  Chloroform:   20  c.c. 

3.  Paraffin-chlorofonn :  a  saturated  solution  (5  grams  of  the  paraffin 
mixture  and  25  c.c.  of  chloroform).  This  solution  is  Hquid  at  room- 
temperature. 

4.  An  embedding  oven  of  block-tin,  with  double  walls  between  which 
is  a  space  to  be  filled  with  water,  f  A  small  gas-burner  is  to  be  placed 
beneath  the  oven.  On  top  there  are  three  openings  ;  two  lead  into  the 
space  between  the  walls,  into  one  a  Reichert  thermo-regulator  %  is  to  be 
inserted,  into  the  other  a  thermometer ;  the  third  opening  leads  into  the 
air  space  of  the  oven  and  into  this  a  second  thermometer  is  to  be  in- 
serted.   The  oven  should  be  25  cm.  long,  15  cm.  high,  and  15  cm.  wide. 

The  embedding  oven  with  its  accessories  is  indispensable  if  much 
embedding  in  paraffin  is  to  be  done  ;  but  the  paraffin  can  be  melted  on  a 
water-bath  and  kept  liquid  with  a  small  spirit  flame. 

5.  An  embedding  frame.  This  consists  of  two  adjustable  bent  metal 
plates,  placed  together 


\  this  way. 


Instead  of  this  frame  little  paper  trays  made  of  stiff  paper  or  cardboard 
can  be  used. 

The  objects  to  be  embedded  must  be  absolutely  free  from  water 
and  to  this  end  should  have  lain  three  days  in  absolute  alcohol  which 
has  been  changed  several  times  ;  they  are  then  transferred  to  a  bottle 
containing  20  c.c.  of  chloroform,  in  which  they  should  remain  until  the 

*  To  be  obtained  from  Dr.  Griibler,  of  Leipzig. 

t  Made  by  R.  Jung,  Heidelberg,  Germany,  and  in  the  United  States  by  the  Eausch  & 
Lomb  Optical  Co.,  New  York. 

%  To  be  obtained  of  the  Bausch  &  Lomb  Optical  Co. ,  New  York. 


APPENDIX.  465 

following  day.  *  From  this  the  objects  should  be  carried  to  the  solution 
of  paraffin  in  chloroform  and  in  from  two  to  eight  hours,  according  to  their 
size,  transferred  to  a  capsule  containing  melted,  but  not  too  hot  paraffin. f 
In  about  a  half  hour  the  objects  are  to  be  transferred  to  a  second  capsule 
with  melted  paraffin,  where,  according  to  their  size,  they  are  to  remain 
from  one  to  five  hours.  %  The  paraffin  should  not  be  heated  more  than 
two  or  three  degrees  above  its  melting  point ;  for  the  mixture  advised 
the  air  in  the  oven  should  have  a  temperature  of  from  50°  to  53°  C. 

When  the  objects  have  been  in  the  paraffin  bath  the  required  length 
of  time,  place  a  slide  in  a  broad  dish  and  on  this  the  embedding  frame, 
into  which  paraffin  and  object  now  are  to  be  poured.  While  the  par- 
affin is  still  fluid  with  a  heated  needle  place  the  object  in  the  desired 
position  ;  so  soon  as  this  is  done  carefully  pour  cold  water  into  the  dish 
until  it  reaches  the  upper  margin  of  the  frame  ;  the  paraffin  will  at  once 
begin  to  solidify,  whereupon  more  water  may  be  added  until  the  entire 
frame  is  submerged.  By  this  manipulation  the  paraffin  hardens  into  a 
homogeneous  mass,  whereas  otherwise  it  is  apt  to  crystallize  and  is  then 
difficult  to  cut  and  also  has  an  injurious  influence  on  the  structure  of  the 
embedded  tissues.  In  about  ten  minutes  the  metal  frames  can  be  re- 
moved ;  the  paraffin  block  should  be  allowed  to  remain  in  the  water  on 
the  slide  until  it  is  completely  solid. 

The  embedded  object  may  be  sectioned  in  a  half  hour.  In  case  it  is 
to  be  used  later  mark  it  with  a  needle.  In  the  paraffin  the  object  can  be 
kept  for  an  indefinite  period. 

THE    CELLOIDIN    METHOD. 

The  celloidin  in  plates  (Grijbler)  has  a  soft  consistence.  The  plates 
are  to  be  cut  in  small  pieces  and  dried  in  the  air,  in  a  place  free  from 
dust ;  they  become  yellow  and  as  hard  as  stone.  Then  16  grams  of  this 
dry  celloidin  are  dissolved  in  100  c.c.  of  absolute  alcohol  plus  100  c.c. 
of  ether.  The  half  of  this  8  per  cent,  solution  is  diluted  with  50  c.c.  of 
absolute  alcohol  plus  50  c.c.  of  ether.  The  half  of  this  4  per  cent,  solu- 
tion is  diluted  with  25  c.c.  of  absolute  alcohol  plus  25  c.c.  of  ether. 

All  three  solutions  should  be  preserved  in  well-stoppered,  wide- 
necked  bottles,  containing  from  i  5  to  20  grams  of  copper  sulfate  that  has 
been  heated  to  white  heat  (p.  20,  No.  3),  and  if  they  become  too  thick  can 
be  diluted  by  adding  equal  parts  of  alcohol  and  ether. § 

*  This  is  sufficient  for  all  cases  ;   for  small  objects  from  one  to  two  hours  will  be  enough. 

I  If  the  paraffin  has  been  melted  on  a  water-bath,  place  the  flame  at  such  a  distance  that 
the  surface  remains  covered  by  a  thin  film  of  solid  paraffin. 

X  This  is  done  in  order  to  remove  all  the  chloroform  from  the  object.  It  is  self-evident 
that  the  same  capsule  must  be  used  for  the  transfer  from  the  paraffin-chloroform.  If  after  fre- 
quent use  the  capsule  contains  much  chloroform,  it  can  be  driven  off  by  stronger  heating  of  the 
paraffin.  So  long  as  the  paraffin  contains  any  chloroform  bubbles  will  rise  on  dipping  in  a 
heated  needle. 

I  After  a  time  the  solutions  become  turbid  and  milky ;  it  is  better  then  to  let  them  dry 
completely  and  to  redissolve  the  pieces  in  the  alcohol-ether  mixture. 
30 


466  HISTOLOGY. 

The  tissues  to  be  embedded  must  be  completely  free  from  water  and 
must  have  lain  one  or  two  days  in  absolute  alcohol  which  has  been 
changed  several  times.  From  this  the  objects  are  transferred  for  twenty- 
four  hours  into  a  mixture  of  equal  parts  of  alcohol  and  ether  and  then 
into  the  2  per  cent.,  the  4  per  cent.,  and  the  8  per  cent,  celloidin  solu- 
tion and  remain  in  each  for  twenty-four  hours.  The  objects  can  remain 
longer  in  the  celloidin  solutions,  but  usually  are  thoroughly  saturated  in 
the  course  of  twenty-four  hours  ;  but  large  objects  enclosing  many  spaces 
must  remain  in  the  thick  solution  about  eight  days.  Each  object  then 
should  be  quickly  placed  on  a  cork  stopper  and  some  celloidin  poured  over 
it.  In  doing  this  care  must  be  taken  not  to  press  the  object  against  the 
cork,  or  it  Avill  easily  become  detached.  There  should  be  a  stratum  of  cel- 
loidin one  or  two  millimeters  thick  between  the  cork  and  the  object.* 
Now  the  whole  is  to  be  placed  under  a  bell-glass,  for  from  one-half  to  four 
hours,  to  slowly  dry  ;  delicate  objects  dry  in  a  half  hour  ;  the  bell-glass 
should  not  be  air-tight,  and  to  prevent  this  should  be  supported  on  one 
side  on  a  needle  or  something  similar. 

When  dry  the  objects  are  placed  in  a  jar  containing  about  30  c.c. 
of  80  per  cent,  alcohol  and  to  keep  them  submerged  glue  the  under 
surface  of  the  cork  stopper  by  means  of  celloidin  to  the  inner  surface  of 
the  Hd  of  the  jar.  On  the  following  day  the  alcohol  should  be  replaced 
by  70  per  cent,  alcohol,  in  which  the  objects  may  remain  an  indefinite 
length  of  time. 

The  celloidin  objects  need  not  be  immediately  mounted.  In  this 
case  take  the  objects  from  the  8  per  cent,  celloidin  solution  and  let  it 
stand  for  several  hours  in  a  tightly  covered  capsule,  until  the  air-bubbles 
in  the  celloidin  have  disappeared.  Then  remove  the  cover  and  let  the 
capsule  with  the  objects  stand  under  a  bell-glass  for  from  6  to  12  hours, 
or  until  a  membrane  has  formed  over  the  surface.  Then  place  the  cap- 
sule with  its  contents  in  70  per  cent,  alcohol  ;  after  24  hours  cut  out  of 
the  solid  celloidin  a  block  containing  the  objects  and  preserve  it  in  70  per 
cent,  alcohol. 

In  order  to  cut  very  thin  sections  the  celloidin  must  be  hardened ; 
for  this  purpose  take  the  objects  embedded  in  celloidin  from  the  70  per 
cent,  alcohol  and  put  them  for  two  days  or  more  into  an  alcohol-glycerol 
mixture  (80  per  cent,  alcohol  one  part,  pure,  concentrated  glycerol  from 
six  to  ten  parts).  The  larger  the  proportion  of  glycerol  to  alcohol,  the 
harder  the  celloidin  becomes  ;  an  extreme  limit  is  one  part  of  alcohol  to 
30  parts  of  glycerol.  Still  greater  difference  in  the  proportions  produces 
strong  curling  of  the  sections.  In  order  to  prevent  the  buckling  of  the 
elastic  celloidin  block  dry  it  carefully  with  filter-paper  when  it  is  removed 
from  the  alcohol-glycerol  mixture,  make  a  pair  of  lateral  incisions  and 
dip  it  into  Hquid  paraffin  ;  such  blocks  cannot  be  preserved  dry,  they 
must  be  returned  to  the  alcohol-glycerol  mixture. 

Preparations  fixed  by  Golgi's  method  require  special  treatment,  since 
the  absolute  alcohol  has  an  injurious  influence  if  the  object  remains  in  it 

*  This  stratum  must  not  be  thicker;  even  well-hardened  celloidin  is  elastic  and  a  thick 
stratum  of  such  elastic  material  would  cause  the  object  to  give  in  sectioning. 


APPENDIX.  467 

beyond  one  hour.  When  the  tissue  is  taken  from  the  silver  solution  it  is 
hardened  in  30  c.c.  of  95  per  cent,  alcohol  for  fifteen  or  twenty  minutes, 
then  in  30  c.c.  of  absolute  alcohol  for  fifteen  minutes,  then  placed  in  the 
thin  celloidin  solution  for  five  minutes.  Meanwhile,  in  the  previously 
smoothed  lateral  surface  of  a  broad  piece  of  elder-pith  make  an  excavation 
just  large  enough  to  take  in  the  zvJwle  preparation  ;  insert  it,  cover  it  with 
celloidin  solution,  fit  a  second  piece  of  elder-pith  on  the  first,  pour  on 
more  celloidin,  and  place  the  whole  for  five  minutes  under  a  bell-glass  to 
dry  ;  then  transfer  it  to  80  per  cent,  alcohol  for  five  minutes  and  cut 
sections  with  a  knife  flooded  with  80  per  cent,  alcohol.  The  microtome 
is  altogether  unnecessary;  satisfactory  sections  can  easily  be  cut  free- 
hand. If  the  microtome  is  used,  the  thickness  of  the  sections  should 
vary  from  40  to  1 20  //.  The  elder-pith  should  be  trimmed  off  so  that 
only  a  small  shell  (i  mm.)  encircles  the  celloidin. 

Sectioning, 
paraffin  objects. 

The  paraffin  block  containing  the  object  is  to  be  secured  in  a  hollow 
cylinder  coated  with  hard  paraffin  (in  the  Thoma  microtome)  or  (in  the 
microtome  of  Miehe)  to  a  little  plate  *  instead  of  the  clamp.  The  plate 
is  simply  warmed  and  the  paraffin  block  glued  to  it  by  pressure.  In 
the  case  of  the  cylinder,  warm  it  and  also  the  base  of  the  paraffin  block  ; 
press  the  latter  lightly  into  the  cylinder  and  by  means  of  a  heated  needle 
inserted  between  them  establish  a  firm  union.  In  order  quickly  to 
solidify  the  paraffin  place  the  cylinder  or  the  plate  for  five  minutes  in 
cold  water.  The  projecting  portion  of  the  paraffin  block  containing  the 
object  should  then  be  trimmed  to  a  four-sided  column,  the  base  of  which 
is  right-angled  square.  The  column  should  not  be  taller  than  one 
centimeter  and  the  object  should  be  encircled  by  a  layer  of  paraffin 
not  over  one  or  two  millimeters  broad. 

The  cylinder  (or  the  plate)  with  the  object  should  now  be  placed 
in  the  microtome.  Sections  are  to  be  cut  with  the  blade  of  the  knife 
dry.      The  position  of  the  knife  depends  on  the  nature  of  the  object. 

Sectioning  zvith  the  knife  placed  obliquely. \  If  the  object  is  large 
and  of  unequal  resistance  the  knife  should  be  so  clamped  that  it  forms  a 
very  acute  angle  with  the  long  axis  of  the  microtome.  The  paraffin 
block  should  so  stand  that  the  knife  strikes  it  first  on  one  corner  of  the 
column.  The  knife  should  be  moved  slowly  and  pressure  upon  it  should 
be  carefully  avoided. 

Sectioning  with  the  knife  placed  transversely.  Screw  the  knife 
down  perpendicular  to  the  long  axis  of  the  microtome,  turn  the  paraffin 
column  so  that  the  blade  will  strike  it  first  on  a  surface.     The  knife  should 

*  Instead  of  the  plate  I  use  cylindric  pieces  of  soft  wood,  about  3  cm.  high  and  1. 5  cm. 
in  diameter,  which  are  screwed  in  the  object  clamp. 

f  In  Miehe's  microtome  the  carrier  of  the  clamp  must  be  changed  to  the  middle  of  the 
instrument,  when  the  knife  is  to  be  placed  obliquely. 


468  HISTOLOGY. 

be  rapidly  moved  with  a  planing  movement  and  then  the  sections  will 
adhere  to  one  another  at  their  edges  and  form  long  ribbons.  When 
the  paraffin  is  of  the  right  consistence  the  first  section  lies  smoothly  on 
the  blade  and  is  shoved  by  the  second  section  in  the  direction  of  the 
back  of  the  knife.  If  however  the  first  sections  show  an  inclination  to 
curl  and  fall  over  the  edge,  they  must  then  be  carefully  held  with  a  deli- 
cate sable  brush  and  led  back  to  the  right  position.  Ribbon-cutting  is 
most  successful  when  the  sections  have  a  thickness  of  o.oi  of  a  milli- 
meter ;  thicker  sections  easily  curl  and  do  not  readily  adhere  to  one 
another  at  their  edges. 

OBSTACLES    IN    SECTIONING    AND    THEIR    REMEDY. 

Every  one  who  has  worked  with  paraffin  is  probably  able  to  explain 
different  unsuccessful  attempts. 

1.  The  knife  glides  over  the  object  and  cuts  a  partial  section  or 
none.  The  reason  for  this  may  lie  in  the  microtome  ;  the  slideway  may 
not  be  clean  ;  examine  the  vertical  portion  of  the  slideway.  Or  the 
knife  is  not  sharp  enough,  or  the  under  surface  has  paraffin  adhering  to 
it ;  in  the  latter  case  remove  the  knife  and  with  a  cloth  wetted  with  tur- 
pentine carefully  cleanse  it.  Knives  with  thin  backs  buckle  if  the  distal 
end  of  the  blade  is  used  ;  thus  it  happens  that  when  the  knife  is  obliquely 
placed  the  blade  cuts  the  object  only  at  the  edge  where  it  first  touches 
and  glides  over  the  rest  without  cutting  it.  In  microtomes  of  earlier 
construction  the  cause  of  this  often  lies  in  the  unsatisfactory  manner  in 
which  the  block  of  paraffin  is  secured. 

Secondly,  the  trouble  may  be  found  in  the  object ;  it  may  be  too 
hard,  or  of  very  unequal  resistance,  or  poorly  embedded  ;  in  the  latter 
case  there  are  two  possibilities.  Either  the  preparation  was  not  thor- 
oughly dehydrated,  in  which  case  it  exhibits  opaque  spots,  or  it  contains 
chloroform  ;  in  this  case  it  is  soft,  and  light  pressure  with  needle  on  the 
surface  leaves  a  mark  or  even  presses  out  fluid.  In  both  cases  the  pro- 
cedure of  embedding  must  be  repeated,  reversing  the  series  of  processes 
to  the  absolute  alcohol  (in  the  latter  case  to  the  paraffin  bath). 

Finally,  the  consistence  of  the  paraffin  may  be  at  fault. 

2.  The  sections  curl.  This  can  be  prevented  by  holding  a  small 
sable  brush  or  bent  needle  lightly  against  the  sections  as  they  are  cut.* 
The  cause  of  this  curling  lies  in  the  hardness  of  the  paraffin,  which  is 
also  responsible  for — 

3.  The  sections  break.  The  usefulness  of  the  paraffin  depends  in  a 
high  degree  on  the  outer  temperature.  If  the  paraffin  is  too  hard  do 
not  endeavor  to  reduce  its  consistence  by  the  admixture  of  soft  paraffin, 
— this  is  the  last  resource — but  employ  simpler  measures.  Cut  the 
sections  near  a  stove  or  near  a  lamp  ;  often  sliglit  warming  of  the  knife 
is  sufficient.  Even  very  good  paraffin  crumbles  when  cut  with  a  cold 
knife. 

*  A  '•  section-smoother  "  for  microtomes  in  which  the  object  is  elevated  vertically  is  made 
by  Kleinert  of  Breslau.  See  further,  Born,  "  Zeitschr.  f.  wissensch.  Mikroskopie,"  Bd.  x,  p. 
157- 


APPENDIX.  469 

4.  The  sections  fold  and  become  pressed  together.  As  a  result  of 
this  the  sectioned  objects  acquire  a  false  outline.  The  reason  for  this  lies 
in  a  too  soft  paraffin.  This  difficulty  may  be  overcome  by  frequently 
placing  the  block  in  cold  water  or  by  cutting  the  sections  in  a  cold  room 
(in  summer,  in  the  morning  hours). 

CELLOIDIN    OBJECTS. 

Trim  the  embedded  object  until  the  enveloping  stratum  of  celloidin 
is  only  one  or  two  millimeters  thick  ;  clamp  the  knife  obliquely,  so  that 
it  makes  a  very  acute  angle  with  the  long  axis  of  the  microtome. 
Moisten  the  blade  with  70  per  cent,  alcohol  by  means  of  a  sable 
brush  ;  this  must  be  done  after  every  second  or  third  section  is  cut. 
The  sections  should  be  removed  with  a  brush  and  transferred  to  a  dish 
containing  70  per  cent,  alcohol.  Very  thin  sections  (less  than  0.02 
mm.)  cannot  be  cut  unless  the  celloidin  has  been  hardened  (p.  465). 

Preserv.atiox  of  Sections. 

PARAFFIN    objects. 

If  the  sections  are  not  very  thin  and  are  not  in  ribbons  they  may  be 
placed  in  a  capsule  with  5  c.c.  of  carbol-xylol  and  when  the  paraffin  is  dis- 
solved transferred  to  a  second  capsule  with  carbol-xylol.  From  this  the 
sections,  if  the  tissue  has  been  stained  in  bulk,  are  carried  to  a  slide  and 
mounted  according  to  the  directions  given  on  page  48.  If  the  sections 
are  unstained  transfer  them  from  the  carbol-xylol  to  5  c.c.  of  ninety-five 
per  cent,  alcohol,  which  is  to  be  changed  in  two  minutes.  In  another 
two  minutes  the  sections  may  be  stained. 

In  the  case  of  serial  sections  and  very  thin  sections,  it  is  necessary 
first  to  glue  the  dry  sections  to  the  slide. 

For  this  purpose  the  slide  must  be  absolutely  clean ;  wash  it  with 
alcohol  and  dry  it  with  a  clean,  not  oily,  cloth  or  place  it  for  a  half  hour 
in  cold  soapsuds.  On  the  well-dried  slide  arrange  the  sections  (or  portion 
of  the  "ribbon"),  and  at  the  edge  of  the  same  place  a  drop  of  distilled 
water  by  means  of  a  delicate  sable  brush.  Another  section  (or  portion  of 
the  ribbon)  is  now  placed  on  the  slide,  another  drop  of  water  added,  and  so 
on  until  the  slide  is  covered.  It  does  not  matter  if  the  sections  float.  Pass 
the  slide  through  a  spirit-flame  or  place  it  for  from  one  to  three  minutes 
in  the  oven  ;  *  on  being  slightly  warmed,  the  sections  spread  out  flat  and 
smooth.  Then  arrange  them  v/ith  a  needle  and  by  slightly  inclining  the 
slide  let  the  water  flow  off  or  absorb  it  with  a  strip  of  filter-paper  and, 
protected  from  dust,  let  the  whole  dry.  On  the  following  day  pour 
carbol-xylol  over  the  slide  and  if  the  sections  are  already  stained  mount 
them  in  xylol-balsam.  In  case  the  sections  are  not  stained  the  carbol-xylol 
is  to  be  wiped  off  and  the  slide  placed  in  ninety-five  per  cent,  alcohol,  t 

*  The  paraffin  must  not  be  allowed  to  melt ;  the  resulting  mixture  of  melted  paraffin  and 
water  is  not  soluble  in  carbol-xylol. 

t  The  carbol-xylol,  also  the  alcohol,  must  be  quickly  wiped  off,  because  the  sections  are 
worthless  if  they  are  allowed  to  become  dry.      Care  must  also  be  exercised  in  placing  the  stain- 


470  HISTOLOGY. 

After  fiv^e  minutes  take  the  slide  from  the  alcohol,  which  is  to  be  quickly 
wiped  off  around  the  sections,  and  either  place  it  in  the  stain  or  cover 
it  with  a  few  drops  of  the  solution,  e.  g.  hematoxylin.  Then  slowly 
transfer  the  slide  to  a  dish  with  distilled  water  and  either  preserve  it  in 
dilute  glycerol  (p.  49),  or  after  the  customary  preliminary  treatment  with 
ninety-five  per  cent,  alcohol  and  carbol-xylol  (p.  50),  mount  it  in  xylol- 
balsam. 

CELLOIDIN    OBJECTS. 

Place  the  sections  in  a  dish  containing  20  c.c.  of  90  per  cent,  alcohol. 
If  the  object  has  not  been  previously  stained  in  bulk,  staining  in  bulk  is 
advisable,  the  sections  may  be  subsequently  stained  ;  but  anilin  colors 
cannot  be  used,  since  they  also  stain  the  celloidin  ;  even  hematoxylin 
imparts  a  light-blue  tint  to  the  celloidin.  The  sections  must  not  be  placed 
in  absolute  alcohol,  since  this  dissolves  the  celloidin  ;  they  are  to  be 
taken  from  the  95  per  cent,  alcohol  and  placed  in  carbol-xylol ;  when  the 
clearing  is  completed  mount  them  in  xylol-balsam. 


Serial  sections  of  celloidin  objects  are  used  only  for  special  purposes, 
for  example,  for  the  central  nervous  system.  See  the  articles  by  Weigert, 
in  the  "  Zeitschrift  fiir  wissenschaftliche  Mikroskopie,"  Bd.  ii.,  p.  490, 
Bd.  iii.,  p.  480,  Bd.  iv.,  p.  209,  and  by  Obregia,  "  Neurologisches  Cen- 
tralblatt,"  Leipzig,  Jahrg.  9,  1890,  p.  195.  The  negative  varnish  rec- 
ommended by  the  former  is  to  be  obtained  of  Dr.  Griibler. 

ing  fluid  on  the  sections,  to  see  that  it  really  covers  them.  Loosening  of  the  sections  occurs  only 
when  there  was  not  enough  water  between  the  section  and  the  slide — the  water  must  be  evenly 
diffused  between  the  two.  The  sections  can  also  be  fastened  to  the  cover-glass  and  this  method 
permits  the  use  of  smaller  quantities  of  the  staining  solution,  alcohol,  and  other  reagents. 


BOOKS  RECOMMENDED   FOR  COLLATERAL  STUDY. 


GENERAL  WORKS. 

KoUiker,  A. — Handbuch  der  Gewebelehre  des  Menschen.     6.  Auflage.     Leipzig  (Engelmann) , 

1896. 
Schafer,  E.  A. — Histology  and  Microscopical  Anatomy,  in  Quain's  Elements  of  Anatomy, 

Tenth  Edition,  London  and  New  York  (Longmans,  Green  &  Co.),  1896. 

SPECIAL  WORKS. 

The  Cell. 

Bergh,  R.  S. — Vorlesungen  iiber  die  Zelle  und  die  einfachen  Gewebe.     Wiesbaden,    1894. 

Henneguy,  L.  F.— Lemons  sur  la  cellule.     Paris  (Carre),  1896. 

Hertwig,  O. — Die  Zelle  und  die  Gewebe.  L  Buch  :  Allgemeine  Anatomic  und  Physiologic 
der  Zelle.  Jena  (Fischer),  1S92.  Translation  published  by  Macmillan,  London  and 
New  York,  1895. 

Wilson,  E.  B. — The  Cell  in  Development  and  Inheritance.  New  York  and  London  (Mac- 
millan), 1896. 

The  Tissues. 

Bergh,  R.  S. — Vorlesungen  iiber  die  Zelle  und  die  einfachen  Gewebe.     Wiesbaden,  1894. 

Hertwig,  O. — Die  Zelle  und  die  Gewebe.  II.  Biich:  Allgemeine  Anatomic  und  Physiologie 
der  Gewebe.     Jena  (Fischer),  1898. 

The  Blood. 
Cabot,  R.  C. — A  Guide  to  the  Clinical  Examination  of  the  Blood  for  Diagnostic  Purposes. 
New  York  (Wood  &  Co.),  1897. 

The  Nervous  System. 
Barker,  L.  F. — The  Nervous  System  and  its  Constituent  Neurones.     New  York  (Appleton  & 

Co. ),  1899. 
Dejerine,  J. — Anatomic  des  centres  nervcux.     Tome  I.     Paris  (Rueff  et  Cie),  1S95. 
Edinger,  L. — Vorlesungen  iiber  den  Bau  der   nervosen  Ccntralorgane.     5.  Auflage.     Leip- 
zig, 1897. 
Gehuchten,  A.   van. — Anatomic  du  systeme  nerveux  de  I'homme.     2  Edition.     Louvain, 

1S97. 
Golgi,  C. — Untersuchungen  iiber  den  fcincrcn  Bau  des  centralen  und  pcripheren  Nervensys- 

tems.     Jena,  1894. 
Lenhossek,  M.  von. — Der  feinere  Bau  des  Nervensystcms  im  Lichte  ncucster  Forschungen. 

2.  Auflage.     Berlin  (Fischer),  1895. 
Ramon  y  Cajal,  S. — Neue  Darstellung  vom  histologischcn  Pau  des  Centralnervensystems. 

(Arch.  Anat.  und  Physiol.,  Anat.  Abth.,  1893). 

Les  nouvellcs  idecs  sur  la  structure  du  systeme  nerveux  chcz  Thommc  et  chez  les 

vertebres.     Paris  (Reinwald  &  Co.),  1894. 

471 


4/2  BOOKS    RECOMMENDED    FOR    COLLATERAL    STUDY. 

The  Intestines. 
Oppel,  A. — Lehrbuch  der  vergleichenden  mikroskopischen  Anatomie  der  Wirbelthiere.     I.  Der 
Magen,  II.  Schlund  und  Darm.     Jena  (Fischer),  1896-1897. 

The  Sensory  Organs. 
Pollitzer,   A. — Die  anatomische  und  histologische  Zergliederung    des    menschlichen  Gehor- 

organs  im  normalen  und  kranken  Zustande.      Stuttgart  (Enke),  1889. 
Ramon  y  Cajal,  S. — La  retine  des  vertebras.     (La  Cellule,  ix,  1893.) 
Schwalbe,  G. — Lehrbuch  der  Anatomie  der  Sinnesorgane.     Erlangen,  1887. 

Technic. 
Apathy,  S. — Die  Mikrotechnik  der  thierischen  Morphologie.      I.  Abtheilung.     Braunschweig 

(Bruhn),  1896. 
Behrens,  W. ,  Kossel,  A.,  und  Schiefferdecker,  P. — Das  Mikroskop  und  die  Methoden  der 

mikroskopischen  Untersuchung.      Braunschweig  (Bruhn),  1889. 
Bohm,  A.,  und  Oppel,  A. — Taschenbuch  der  mikroskopischen  Technik.      3.  Auflage.     Miin- 

chen  (Oldenbourg),  1896. 
Lee,  A.  B. — The  Microtomist's  Vade-mecum.     A  Handbook  of  the  Methods  of  Microscopic 
Anatomy.     Third  Edition.     Philadelphia  (Blakiston),  1900. 


INDEX. 


A. 

Acer\ailus  cerebri,  209,  233 
Acetic  acid,  20 
Achromatin,  65 
Acid  alcohol,  25 
"    fuchsin,  26 
"    mixture,  24 
Adenoid  tissue,  95,  145,  147 
of  the  intestines,  277 
of  the  lymph-glands,  143 
of  the  pharynx,  262 
of  the  stomach,  277 
of  the  thymus,  317 
of  the  tongue,  259 
Adipose  tissue,  92,  102 
Adrenal  body,  227 
Agminated  nodules,  278,  302 
Alcohol,  20,  31,  35 

acid,  25 

one-third,  20 
Alcohol-ether  mixture,  464 
Alcohol-glycerol  mixture,  465 
Alum-carmine,  25,  39 
Alum-cochineal,  25 
Alveolar  ducts,  310 
Amakrines,  409 
Ameboid  movement,  68 
Ameloblasts,  255 
Amitosis,  69,  394 
Ammonium  picrate,  26,  42 
Amphipyrenin,  65 
Anaphase,  71 

Anisotropic  substance,  107 
Apparato  reticulare,  64,  115 
Appendix  epididymidis,  345 

testis,  345 

vermiformis,  276 
Arachnoid,  210 

granulations  of,  210 
Archoplasm,  65,  350 
Arcuate  fibers,  400 
Arcus  tarseus,  427 

"  "        externus,  427 

Areolar  tissue,  94 
Arrectores  pilorum,  379 
Arteries,  128 

classification  of,  128 
Astrocyte,  196 
Astrosphere,  69 
Auditory  sand,  438 
Auerbach's  plexus,  281,  303 
Axis-cylinder,  116 
Axon,  116 
Axoneurons,  190 
Axoplasm,  121 


B. 

Baillarger's  stripes,  200 
Bartholin's  duct,  245 
Basal  corpuscle,  76 
Basement  membrane,  86,  94 
Berlin  blue,  48 
Bile,  295 

Bile  capillaries,  290 
Bioblasts,  64 
Blood,  136 

cells  of,  136,  137 

crystals  of,  140 

development  of  the  cells  of,  140 

-duct,  139 

elementary  granules,  139 

examination  of,  for  legal  purposes,  156 

fibrin,  139 

hemoglobin,  136,  139 

plasma,  136 

-platelets,  139 

technic,  154,  155,  156,  157 
Blood-vessel  system,  126 
arteries,  128 
capillaries,  134 
heart,  126 

lymph-spaces  of,  136 
nerves  of,  135 
technic,  152,  153 
veins,  132 
Bone-cells,  99 
Bones,  160 

articulations  of,  165 

blood-vessels  of,  165 

development  of,  168 

endochondral  formation,  170 

endosteum,  162 

growth  of,  1 75 

haversian  canals,  161 

haversian  systems,  162 

Howship's  lacunae,  177 

lamellsE  of,  161 

lymph-vessels  of,  165 

marrow  of,  162,  164 

metaplastic  formation,  174 

neoplastic  formation,  174 

nerves  of,  165 

osteoblasts,  100,  172 

ostoclasts,  163,  177 

perichondral  formation,  173 

periosteum,  16^ 

primary,  170 

resorption  of,  176 

secondary,  174 

Sharpey's  fibers,  98,  164 

technic,  177 


47: 


474 


INDEX. 


Bones,  Volkmann's  canals,  162,  165 
Bowman's  capsule,  323 
glands,  455 
"  membrane,  399 

Brain,  197 

cerebellar  cortex,  202 

cerebral  cortex,  198 

ganglia -of,  202 

Golgi  staining  of,  232 

hypophysis  cerebri,  208 

neuroglia  of,  201,  207 

pineal  body,  208 

technic,  232,  233 

ventricles  of,  202 

white  substance  of,  207 
Brain-sand,  209,  233 
Bronchi,  309,  311 

blood-vessels  of,  315 

cartilages  of,  311 

glands  of,  312 

mucosa  of,  312 

muscle-fibers  of,  311 

technic,  319 
Brunner's  glands,  275 
Brushborder,  76,  324 
Budding,  72 

Bulbourethral  glands,  346 
Bundle  of  Vicq  d'Azyr,  201 
Bursse,  185 

C. 

Cajal's  cells,  198 
Calcification,  center  of,  171 
Calices,  renal,  329 
Canada  balsam,  23 
Canalized  fibrin,  366 
Capillaries,  bile,  290 

blood-vessel,  134 

lymph-vessel,  141 

secretory,  86 
Carbol-xylol,  23,  50 
Cardiac  muscle,  105 
Carmalum,  25,  39 
Carmine,  alum-,  25,  39 

borax-,  25,  40 

neutral,  24,  39 
Carotid  gland,  136 
Cartilage,  95 

capsule,  95 

cells,  97 

chondrin,  96 

elastic,  97 

fibrous,  98 

hyaline,  96 

technic,  104 
Cartilages,  168 

articular,  168 

bronchial,  311 

costal,  168 

epiphyseal,  175 

perichondrium,  168 
Caruncula  lacrimalis,  427 
Cell-membrane,  66 
Celloidin,  464 
Cells,  60,  63 

acid,  267 


Cells,  albuminous,  240 
amakrine,  409 
basal,  455 

basal  corpuscle  of,  76 
basket,  86,  205 
blood-,  136 
bone,  99 
border-,  242 
Cajal's,  198 
canaliculi  of,  64 
cartilage,  97 
centroacinar,  283 
chief,  267 

chromaf&ne,  220,  228 
Claudius's,  444 
collecting  center  of,  81 
column,  191 
commissure,  191 
concentric,  196,  408 
cone-visual,  411 
connective-tissue,  92 
cover-,  459 
decidual,  361 
Deiters's,  117,  196,  443 
egg-,  348 
enamel,  254 
endothelial,  76 
ependymal,  195 
epithelial,  75 
fat,  93 

fat,  serous,  93 
fiber,  437 
fixed,  93 
form  of,  67 
ganglion,  113 
giant,  163 
gland.  So 

glia,  195 

goblet,  81,  273 

granule,  203 

gustatory,  459 

hair,  437,  443 

Hensen's,  444 

hepatic,  291 

indifferent,  60 

internal,  193 

interstitial,  337 

Langerhans's,  221 

liver,  291 

long-rayed,  196,  201 

lutein,  352 

marginal,  192 

marrow,  162 

mast-,  93 

moss}^  196 

mucin,  240 

mucous,  241 

muscle-,  104 

nerve-,  113 

networks  of,  64 

olfactory,  455 

Paneth's,  272 

parietal,  267 

pigment,  76,  376,  380,  412 

pillar,  442,  443 

plasma,  93 

plurifunicular,  192 


INDEX. 


475 


Cells,  polar  differentiation  of,  63 
polymorphous  nerve-,  200 
prickle,  79 
pseudopodia  of,  68 
Purjcinje's,  204 
pyramidal,  198 
reproduction  of,  68 
rod-visual,  411 
secretory  products  of,  72 
semen-,  340 
serous,  241 
Sertoli's,  339 
short-rayed,  196,  201 
size  of,  67 
spider,  196 
sperm,  340 
structure  of,  63 
tactile,  221 
taste,  459 
tegmental,  459 
tendon,  183 
trophospongium  of,  64 
union  of,  73 
vasoformative,  154 
vital  properties  of,  67 
wandering,  93,  137 
Cell-division,  68 
Cell-knots,  366 
Cell-membrane,  66 
Cell-nets,  64 
Cement-substance,  73 
Central  corpuscle,  65 
Central-spindle,  70 
Centriole,  65 
Centrosome,  65 
Cerebellar  cortex,  202 

basket  cells  of,  205 
cells  of  Purkinje,  204 
ganglionic  stratum,  204 
granule  layer  of,  203 
gray  stratum  of,  205 
neurogha  of,  207 
staining  of,   233 
Cerebral  cortex,  198 

bundle  of  Vicq  d'Azyr,  201 
cells  of  Cajal,  198 
interradial  reticulum,  200 
molecular  zone,  198 
neuroglia  of,  201 
radiating  bundles  of,  200 
staining  of,  232 
stripe  of  Gennari,  200 
substantia  reticularis  alba,  201 
superradial  reticulum,  200 
tangential  fibers,  198 
zone  of  large  pyramidal  cells,  200 
zone  of  polymorphous  cells,  200 
zone  of  small  pyramidal  cells,  198 
ganglia,  202 
Cerumen,  450 
Ceruminous  glands,  449 
Chondrin,  96 
Choriocapillaris,  402 
Choroid,  402 

boundary  zone  of,  402 
lamina  basalis,  403 

"       choriocapillaris,  402 


Choroid,  lamina  vasculosa,  402 
stroma  of,  402 
tapetum  cellulosum,  402 
"        fibrosum,  402 
Chromaffine  cells,  219,  220,  228 
Chromatin,  65 
Chromic  acid,  21,  32 
Chromic-acetic  acid,  22 
Chromic-acetic-osmic  acid,  22,  34 
Chromosomes,  69 
Chyle,  146 
Ciliary  body,  403 
"        muscle,  404 
"        processes,  403 
Cihated  epithelium,  78 
Clearing,  50 
Coccygeal  gland,  136 
Cochineal,  25 
Cochlea,  43S 
Cohnheim's  fields,  109 
Coil-glands,  389 

distribution  of,  389 
secretion  of,  389 
Collagen,  90 
Collastin,  90 

Collateral  fibers,  112,  117 
Colloid,  316 
Colored  blood  corpuscles,  136 

development  of,   140 
hemoglobin,  136 
stroma  of,  136 
Colorless  blood  corpuscles,  137 

development  of,  140 
granules  of,  13S 
varieties  of,  138 
Colostrum  corpuscles,  393,  395 
Common  bile-duct,  287 
Compact  bone,  160 
Cone-fiber,  411 
Cone-granule,  411 
Congo  red,  25,  300 
Conjunctiva,  palpebral,  425,  426 

"  scleral,  427 

Conjunctival  recesses,  427 
Connective  tissue,  89 
bone,  174 
bundles,  89 
cells  of,  93 
collagen,  90 
elastic,  90 
fibrillar,  89 
glutin,  90 

intercellular  substance  of,  89 
lymph-spaces  of,  100 
mucous,  89 
nerves  of,  100 
reticular,  94 
technic,  loi,  102,  103 
vessels  of,  100 
wandering  cells  of,  93 
Conus  medullaris,i89 
Cornea,  399 

anterior  basal  membrane,  399 
arcuate  fibers,  400 
blood-vessels  of,  422 
canaliculi  of,  400 
cells  of,  400 


476 


INDEX. 


Cornea,  endothelium  of,  401 

epithelium  of,  399 

nerv'es  of,  423 

posterior  basal  membrane,  401 

spaces  of,  400 

substance  proper,  399 

technic,  432,  433 
Corona  radiata,  351 
Corpora  quadrigemina,  198 

"        striata,  198 

Corpus  Highmori,  336 

"       luteum,  352 

"       pineale,  208 

Corpuscles,  articular,  224 

epithelial,  317 

genital,  224 

Grandry's,  221 

Hassal's,  318 

Herbst  and  Key-Retzius's,  224 

lamellar,  222 

Malpighian,  148,  321 

Merkel's,  221 

Pacinian,  222 

renal,  321 

tactile,  224 

Vater's,  222 

Wagner  and  Meissner's,  224 
Corpuscula  amylacea,  209,  233 
Cover-glass  cement,  23,  49,' 50 
Cover-glasses,  18 
Cowper's  glands,  346 
Cox-Golgi  method,  45 
"        "      mixture,  22 
Crusta,  66 

Cumulus  oophorus,  351 
Cupula,  438 
Cuticula,  66 
Cystic  duct,  287 
Cytoblastema,  68 
Cytogenous  tissue,  95 
Cytolinin.  64 


Dahlia,  alum-carmine,  26 
Daughter-stars,  71 
Decalcification,  36 
Decidua  graviditatis,  359 

menstrualis,  358 

placentalis  subchorialis,  366 

refiexa,  360 

serotina,  359 

vera,  360 
Decidual  cells,  361 
Dehydrating,  50,  463,  465 
Demilunes,  242,  245 
Dendrites,  112,  117 
Dentine,  100 

Descemet's  membrane,  401 
Deutoplasm,  350 
Diarthroses,  166 
Diplosome,  66 
Direct  cell-division,  69 
Dissection,  28,  29 
Ductulus  aberrans,  345 
Duodenum,  270 
crypts  of,  271 


Duodenum,  glands  of,  272,  275 

villi  of,  271 
Dura,  209 
Dyaster,  71 

E. 

Ear,  436 

arcus  spiralis,  442 

arteries  of,  445 

auditory  hair,  437 

auditor}'  sand,  438 

auditory  teeth,  440 

bony  labyrinth,  437 

cells  of  Claudius,  444 

cells  of  Deiters,  443 

cells  of  Hensen,  444 

ceruminous  glands,  449 

cochlea,  438 

cristae  acusticae,  437 

cupula,  438 

ductus  cochlearis,  437 

ductus  endolymphaticus,  448 

ductus  perih'mphaticus,  448 

ductus  reuniens,  437 

ductus  semicirculares,  436 

ductus  utriculo-saccularis,  436 

endolymph,  437,  439 

eustachian  tube,  488 

external,  448 

fiber-cells,  437 

foramina  nervina,  441 

gangHon  spirale,  445 

hair-cells,  437,  443 

internal,  436 

labium  tympanicum,  438 

labium  vestibulare,  438 

lamina  spiraUs  membranacea,  441 

hgamentum  spirale,  439 

limbus  spiralis,  438,  440 

lymph  paths  of,  448 

maculce,  437 

membrana  basilaris,  441 

membrana  reticularis,  444 

membrana  tectoria,  445 

membrana  vestibularis,  438 

membranous  labyrinth,  437 

middle,  448 

nerves  of,  445 

Nuel's  space,  444 

otoconia,  438 

otoliths,  438 

perilymph,  437 

pillar-cells,  442 

Reissner's  membrane,  438 

saccule,  437 

semicircular  canals,  437 

spiral  body,  443 

spiral  ligament,  439 

spiral  organ,  442 

strije  vascularis,  439 

sulcus  spiralis,  438 

technic,  450,  451 

tunnel,  442 

tympjanum,  448 

utricle,  437 

vas  prominens,  439 

vas  spirale,  447 


INDEX. 


477 


Ear,  veins  of,  446 

vestibular  membrane,  43Q 

zona  pectinata,  442 

zona  perforata,  441 

zona  tecta,  442 
Egg  protoplasm,  350 
Ehrlich's  dry  method,  154 
Elacin,  90 
Elastic  tissue,  91 
Elastin,  90 
Eleidin,  376 
Elementary  granules,  139 

"■  organism,  63 

Embedding,  463 

in  celloidin,  464 

in  liver,  37 

in  paraffin,  463 
Enamel  prisms,  249 
Endaxoneurons,  191 
End-bulbs,  222,  224 
Endogenous  cell-formation,  72 
Endothelia,  76 
Eosin,  25,  39 

Ependyma  of  the  ventricles,  202 
Epicerebral  space,  211 
Epididymis,  341 
Epiglottis,  308 
Epiphysis,  208 
Epithelium,   75 

brushborder  of,  76 

cells  of,  75,  76 

ciliated,  78 

crusta  of,  75 

cubical,  75 

cuticula  of,  76 

cylinder,  77 

distribution  of,  77,  78 

germinal,  of  ovary,  348 

gland-cells,  80 

glandular,  82 

goblet-cells  of,  81 

isolation  of,  29 

many -rowed,  77 

neuro-,  76 

of  lens,  418 

of  mucous  membranes,  239 

pavement,  75 

pigmented,  75,  76 

prickle-cells  of,  79 

respiratory,  312 

secretory  activity  of,  80 

sensory,  76 

squamous,  76 

terminal  bars  of,  79 

transitional,  330 
Eponychium,  378 
Epoophoron,  353 
Ergastoplasm,  80 
Erythroblasts,  140 
Erythrocytes,  136 
Esophagus,  263 
Eustachian  tube,  448 
Exoplasm,  63 
Eyeball,  398 

angle  of  iris,  405 

blood-vessels  of,  420 

canal  of  Cloquet,  420 


Eyeball,  canal  of  Petit,  419 

canal  of  Schlemm,  422 

choroid,  402 

ciliary  body,  403 

contents  of,  398 

cornea,  399 

development  of,  399 

iris,  404 

lamina  fusca  sclera,  401 

lamina  suprachorioidea,  401 

lens,  417 

lymph-paths,  423 

nerves  of,  423 

optic  nerve,  416 

retina,  406 

sclera,  401 

technic,  429 

venae  vorticosae,  422 

vitreous  body,  419 

zonula  ciliaris,  419 
Eyelashes,  425 
Eyelid,  424 

blood-vessels  of,  427 

caruncula  lacrimalis,  427 

cilia,  425 

glands  of,  426-427 

lymph-vessels  of,  427 

muscles  of,  426 

nerves  of,  428 

ocular  conjunctiva,  427 

palpebral  conjunctiva,  425 

plica  semilunaris,  427 

tarsus,  426 

technic,  436 

third,  427 

F. 

Fallopian  tube,  353 
Fasciae,  185 

Fenestrated  membranes,  91 
Fiber,  spiral,  217,  341 
Fibers,  arcuate,  400 

cone-,  411 

intergemmal,  461 

intragemmal,  461 

lattice-,  294 

lens-,  417 

moss-,  207 

rivet-,  79 

rod-,  411 

stem-,  192 

tangential,  198 
Fiber-apparatus,  411 
Fiber-basket,  40S 
Fiber-cell,  437 
Filar-mass,  64 
Fixation  of  tissues,  3 1 
Flemming's  mixture,  22,  34 
Formaldehyde,  32 
Formic  acid,  23 
Formol,  21 

Fornix  conjunctivae,  427 
Fresh  objects,  examination  of,  52 


G. 


j  Gall-bladder,  287 
f  Ganglia,  214 


478 


INDEX. 


Ganglia,  cerebral,  19S 

spinal,  214 

S3'mpathetic,  217 
Ganglion  cells,  113 

apolar,  114 

bipolar,  113 

multipolar,  113 

unipolar,  113 
Ganglion  spirale,  445 
Ganglio  neurons,  190 
Gastric  glands,  267 

"       pits,  267 
Gemmation,  72 
Generatio  sequivoca,  68 
Genitalia,  external,  346,  368 
Gennari's  stripes,  200 
Germ-layers,  60 
Giannuzzi's  demilunes, ^242 
Gitterfasern,  294 
Gitterwerkes,  294 
Glacial  acetic  acid,  20 
Glands,  82 

accessory  tear-,  426 

albuminous,  242 

areolar,  394 

Bartholin's,  369 

Bowman's,  455 

Brunner's,  275 

bulbourethral,  346 

cardiac,  264 

carotid,  136 

ceruminous,  449 

ciliary,  426 

coccygeal,  136 

coil,  389 

Cowper's,  346 

dehiscent,  85 

duodenal,  275 

fundus,  267 

gastric,  267 

Harder's,  436 

intestinal,  272 

labial,  246 

lacrimal,  428 

Lieberklihn's,  272 

lingual,  242,  244 

Litri's,  333 

lymph,  142 

mammary,  392 

Meibomian,  426 

mixed,  244 

Moll's,  426 

Montgomery's,  394 

mucouS;  244 

Nuhn's,  246 

olfactory-,  455 

parotid,  243 

peri-urethral,  332 

preputial,  389 

pylorus,  268 

sebaceous,  388 

secretory  capillaries  of,  86 

serous,  242 

subhngual,  244 

submaxillary,  245 

sudoriparous,  389 

sweat-,  389 


Glands,  tarsal,  426 

tear,  428 

trachoma,  427 

Tyson's,  389 

urethral,  333 
Glomus  caroticum,  136 
"       coccygeum,  136 
Glutin,  90 
Glycerol,  23,  49 
Goblet-cells,  81,  273 
Gold  chlorid,  23,  47 
Golgi's  method,  45 

"  "        modification  of,  47 

"       mixture,  21 
Golgi-net,  iiS 
Graafian  follicles,  351 
Granula,  64,  81 
Ground-substance,  73 
Gustatory  organ,  458 

H. 

Haftfasern,   79 
Hairs,  378 

color  of,  380 

development  of,  383 

elements  of,  379 

follicles  of,  378,  380 

growth  of,  386 

shedding  of,  386 

structure  of,  378 

technic,  396 
Hair-follicles,  378 

dermal  sheath,  379,  381 

glands  of,  388 

inner  root-sheath,  381 

muscles  of,  379 

outer  root-sheath,  381 
Hardening  of  tissues,  35 
Haversian  canals,  161 

"         lamellae,  161 
Heart,  126 

annuli  fibrosi,  127 

blood-vessels  of,  128 

endocardium,  126 

epicardium,  127 

lymph -vessels  of,  128 

myocardium,  126 

nerves  of,  128 

pericardium,  128 

Purkinje's  fibers,  128 

technic,  152 

valves  of,  127 
Heidenhain's  iron-hematoxylin  method,  44 
Hemalum,  39 

Hematoblasts,  140,  164,  319 
Hematoidin  crystals,  139,  157 
Hematokonia,  139 
Hematoxylin,  Delafield's,  24,  42 

Hansen's,  23,  38 

Heidenhain's  iron-,  44 

Mallory's,  24,  44 

Weigert's,  24 
Hemin  crystals,  139,  156 
Hemoglobin,  136,  139 

"  crystals,  157 

Hermann's  mixture,  22,  34 
Howship's  lacunae,  177 


INDEX. 


479 


Huschke's  teeth,  440 
Hyaloid  canal,  423 

"         membrane,  94 
Hydatid  of  Morgagni,  345 
Hydrochloric  acid,  21 
Hypophysis  cerebri,  20S 


Idiosome,  65 
Illumination,  central,  55 

"  lateral  or  oblique,  55 

Impregnation,  silver,  45 
Indirect  cell-division,  69 
Injecting,  48 
Instruments,  17,  iS,  19,  463 

care  of,  29 
Intercellular  bridges,  79 

"  substance,  61,  73 

Intertilar-mass,  64 
Intermediate  lacunae,  148 
Interstitial  cells,  337 

"  granules,  109 

"  tissue,  94 

Intervillous  spaces,  365 
Intestine,  270,  275 

blood-vessels  of,  278 

crypts  of  large,  2  75 

epithelium  of,  272 

goblet-cells  of,  273,  275 

intestinal  glands,  272 

Lieberkiihn's  crypts,  272 

lymph-nodules  of,  277 

lymph-vessels  of,  280 

ner\^es  of,  280 

plicae  circulares,  270 

technic,  301,  302,  303 

tunics,  270,  275 

valvulae  conniventes,  270 

villi  of  small,  271 
Involuntary  muscle,  104 
lodin-alcohol,  ^7, 
Iris,  404 

Iron  solution,  22 
Iron-hematoxylin,  44 
Isolation,  29 
Isotropic  substance,  107 

K. 

Karyokinesis,  69 
Karyosomes,  63 

Keratohyaline  granules,  376,  3S0 
Kerkring's  valves,  270 
Kidney,  321 

blood-vessels  of,  327 

brushborder,  76,  324 

capsule  of  the  glomerulus,  323 

connective  tissue  of,  325 

glomerulus,  323 

Henle's  loop,  321,  324 

lymph-vessels  of,  328 

medullary  rays,  322 

nerves  of,  328 

papillae  of,  321 

papillary  duct,  321 

renal  corpuscle,  323 


Kidney,  technic,  ;};i^ 

tunica  albuginea  of,  325 
uriniferous  tubules,  321,  323 

Kopsch's  fluid,  21,  33 


Labra  glenoidalia,  166 
Lacrimal  canaliculi,  429 
"         duct,  naso-,  429 
"         gland,  428,  436 
"         sac,  429 
Lacunae,  of  bone,  98 

Howship's,  177 

intermediate,  148 
Lamellar  corpuscles,  222 
Lamina  cribrosa,  417 
"        fusca  sclerae,  401 
"       suprachorioidea,  401 
Lanterman's  notches,  121 
Lanugo  hairs,  380,  388 
Laiy-nx,  308 

blood-vessels  of,  308 

cartilages  of,  308 

glands  of,  308 

lymph-vessels  of,  308 

nerves  of,  309 
Larynx,  solitary  nodules  of,  308 

technic,  319 

vocal  cords,  308 
Lens,  417 

-capsule,  419 

development  of,  417 

epithelium  of,  418 

-fibers,  417 

-stars,  418 

technic,   434,  435 
Leucocytes,  137 

classification  of,  138 

development  of,   140 

granules  of,  138 

technic,  154 
Lieberkiihn's  crypts,  272 
Ligamentum  iridis  pectinatum,  406 
Ligamentum  spirale,  439 
Lingual  tonsils,  259 
Linin,  65 
j  Lithium  carbonate,  24 
I  Litri's  glands,  333 
Liver,  2  84 

bile-capillaries,  287,  290 

blood-vessels  of,  292 

capsule  of,  294 

cells  of,  291 

hepatic  duct,  287 

hepatic  trabeculas,  2S5 

interlobular  bile-ducts,  287 

interlobular  connective  tissue,  288 

lobules  of,  288 

lymph-vessels  of,  294 

nerves  of,  295 

secretion  of,  295 

technic,  306,  307 

vasa  aberrantia,  287 
Lungs,  309 

alveolar  ducts,  310,  313 


48o 


INDEX. 


Lungs,  alveoli,  310,  313 

blood-vessels  of,  314 

elastic  fibers  of,  313 

infundibula  of,  310 

interlobular  tissue  of,  314 

lobules  of,  310 

lymph-vessels  of,  315 

muscle-fibers  of,  311 

nerves  of,  315 

pigmentation  of   314 

pleura,  314 

respiratory  bronchioles,  312 

respiratory  epithelium,  312 

technic,  319,  320 

terminal  vesicles,  310 
Lunula,  378 
Lymph,  100,  146 

"         canaliculi,  141 
"         capillaries,  141 
"         corpuscles,  138 
"        spaces,  100 
Lymph  tissue,  95,  143,  145,  147 
Lymph-glands,  142 

blood-vessels  of,  144 

germinal  center,  143 

lymph-vessels  of,  143 

nerves  of,  145 

structure  of,  143 

technic,  158 
Lymph-nodules,  peripheral,  145 
Lymphocytes,  138 
Lymph-spaces,  adventitial,  136,  211 

pericellular,  211 

perivascular,  211 
Lymph-vessels,  141 

origin  of,  141 

stomata  of,  141,  142 


M. 

Macula  lutea,  412 
Malpighian  corpuscle  of  kidney,  321 
"  "  of  spleen,  148 

Mammary  gland,  392 

areolar  glands,  394 
cells  of,  393 

colostrum  corpuscles,  393 
during  lactation,  393 
during  pregnancy,  393 
secretion  of,  395 
technic,  398 
Margarin  crystals,  93 
Marrow,  162 

elements  of,  162,  163 
gelatinous,  162 
red,  162 
yellow,  162 
Mast-cells,  93 

Measurement,  microscopic,  58 
Medullary  rays,  322 
Megakaryocyte,  163 
Meissner's  plexus,  281,  303 
Membrana  basilaris,  441 
"  chorii,  364 

"  granulosum,  351 

"  limitans  interna,  407 

"  limitans  iridis,  405 


Membrana  limitans  olfactoria,  455 

"  propria,  86,  94 

"  reticularis,  444 

"  tectoria,  445 

"  vestibularis,  438 

Menisci,  166 
Metakinesis,  71 
Metaphase,  70 
Metaplasia,  100 
Methylene-blue,  26,  42 
Methyl-violet  B,  26,  41 
Micron,  67 
Microscope,  care  of,  17 

management  of,  55 
Microsomes,  63 
Microtome,  463 
Milk,  human,  395 
"      witches',  395 
Mitochondria,  63 
Mitom,  64 
Mitosis,  69 

in  the  intestines,  272 

in  the  lymph-glands,  143 
Moist  chamber,  53 
Molecular  motion,  68 
Monaster,  71 
Mother-star,  71 
Mounting,  48,  468 
Mucous  corpuscles,  261 
crypts,  358 
"         glands,  241,  244 
"        membrane,  structure  of,  239 
Mliller's  fluid,  21,  33 
Muller-formol  mixture,  21,  33 
Muscles,  182 

perimysia,  182 

technic,  185 
Muscle-buds,  226 
Muscle-columns,  108 
Muscle-fibers,  104 

branched,  107 

cardiac,   105 

Cohnheim's  fields,  109 

fibrillae  of,  106,  107 

nuclei  of,  104,  105,  109 

pale,  109 

red,  109 

sarcolemma,  109 

sarcoplasm,  106,  108 

smooth,  104 

striated,   106 

technic,  no 
Muscle-spindle,  226 
Myelin,    112,  121 
Myelocytes,  140,  162 


N. 

Nails,  377 

elements  of,  378 
eponychium,  378 
growth  of,  378 
lunula,  378 
matrix  of,  377 
technic,  396 

Nerve-cells,  112 
apolar,  114 


INDEX. 


481 


Nerve-cells,  apparato  reticulare  of,  115 

bipolar,    113 

canaliculi  of,  115 

dendrites,  112 

fibrils  of,  114 

first  type,  117 

granules  of,  115 

multipolar,  113 

second  type,  118 

technic,  122 

trophospongium  of,  115 

unipolar,  113 
Nerve-endings,  220 

end-bulbs,  222,  224 

in  epithelium,  220 

in  smooth  muscle,  227 

in  striated  muscle,  226 

motor,  226 

muscle-spindle,  226 

sensory,  220 

tactile-cells,  221 

tactile  corpuscles,  224 

technic,  235,  236,  237,  238 

tendon-spindle,  225 

terminal-cylinder,  226 
Nerve-felt,  189 
Nerve-fibers,  118 

axis-cylinder,  ti6 

internodes,  122 

medullary  sheath  of,  121 

medullated,  120 

myelin,  121 

neurilemma,  122 

nodes  of,  121 

nonmedullated,  119 

technic,  123,  124,  125 
Nerve-lattice,  118 
Nerve-process,  112 
Nerves,  212 

blood-vessels  of,  213 

cerebro-spinal,   212 

endoneurium,  212 

epineurium,  212 

fiber-sheaths,  212 

lymphatics  of,  213 

perineurium,  212 

sympathetic,  213 

technic,  234 
Net  knots,  65 
Neurilemma,  122 
Neuroblasts,   112 
Neurodendron,  112 
Neuro-epithelium,  76 

of  ear,  437,  442,  443 

of  nose,  455 

of  retina,  411 

of  taste-buds,  459 
Neuroglia,  122,  195,  201 
Neuron,  112 
Neuropilem,  118,  189 
Neuroplasm,  121 
Nissl's  bodies,  115 
Nitric  acid,  20,  32 
Nodes  of  Ranvier,  121 
Normal  salt  solution,  20 
Nuclear  sap,  65 
"         spindle,   70 
31 


Nuclein,  65 
Nucleolus',  65 
Nucleus,  65 
Nuel's  spaces,  444 
Nuhn's  gland,  246 


O. 


Ocular-micrometer,  58 
Odontoblasts,  100,  250,  256 
Olfactory  organ,  453 

blood-vessels  of,  457 
buds,  457 
cells  of,  455 
glands  of,  455 
h'mph  vessels  of,  457 
mucous  membrane  of,  454 
nerves  of,  456 
olfactor}^  region,  454 
respirator}'  region,  453 
technic,  457 
vestibular  region,  453 
membrana  hmitans  olfactoria,  455 
Omentum,  296 
Optic  nerve,  416 

lamina  cribrosa,  417 
Optic  thalami,  198 
Ora  serrata,  414 
Orange,  25,  39 
Orth's  mixture,  21,  33 
Osmic  acid,  22,  34 
Osmio-bichromate  mixture,  21,  45 
Osseous  tissue,  98 
Osteoblasts,  100,  172 
Ostoclasts,   163,   177 
Otoconia,  438 
Otoliths,  438 
Ovary,  348 

blood-vessels  of,  353 
corpus  luteum   352 
germinal  epithehum,  348 
lymph -vessels  of,  353 
nerves  of,  353 
primitive  follicles,  349 
stroma  of,  348 
technic,  37o..37i 
tunica  albuginea  of,  348,  371 
vesicular  follicles,  351 
Oviduct,  353 
Ovula  Nabothi,  358 
Ovum,  350 

corona  radiata,  351 
deutoplasm,  350 
germinal  spot,  350 
germinal  vesicle,  350 
oolemma,  350 
vitellus,  350 
zona  pellucida,  350 


Pacchionian  bodies,  210 
Pacinian  corpuscles,  222 
Palate,  soft,  261 
Palatine  tonsils,  262 
Pal's  method  for  medullated  nerves,  230 
mixture,  24 


482 


INDEX. 


Pancreas,  2S2 

centroacinar  cells,  2S3 

intertubular  cell-grovips,  284 

technic,  305 

zymogen  granules,  283 
Paneth's  cells,  272 
Panniculus  adiposus,  374 
Papillae,  257,  373 
Papillary  body,  427 
Paracarmine,  25,  41 
Paradidymis,  345 
Paraffin,  463 

Paraffin-chloroform  mixture,  463 
Paraganglia,  220 
Paranuclein,  65 
Paranucleus,  66 
Paraxon,  117 
Pareleidin,  376 
Paroophoron,  353 
Parotid  gland,  243 
Pellicula,  66 
Pelvis  of  kidney,  329 
Penis,  346 

arteries  of,  346 

corpora  cavernosa,  346,  347 

erectile  tissue  of,  346 

helicine  arteries,  346 

tunica  albuginea  of,  346 

veins  of,  347 
Perichondrium,  168 
Perilymph,  437 
Periosteum,  164 
Peritoneum,  295 
Peyer's  patches,  278 
Pfiiiger's  demilunes,  242 
Phagocytes,  68 
Pharyngeal  tonsil,  262 
Pharynx,   261 

Phosphomolybdic  acid,  22,  24 
Pia,  210 
Picric  acid,  22 
Picrocarmine,  24,  41,  53 
Picrofuchsin,   26,  43 
Pineal  body,  208 
Pituitary  body,  208 
Placenta,  362 

blood-vessels  of,  365,  367 

canalized  fibrin,  366 

cell-knots,  366 

decidua  placentalis  subchorialis,  366 

foetalis,  362 

intervillous  spaces,  365 

membrana  chorii,  364 

septa  of,  366 

syncytium  of,  365 

technic,  372 

uterina,  362 

villi  of,  365 
Plasma-cells,  93 
Plasmasomes,  63 
Plastin,  63 

Platinum-acetic-osmic  mixture,  22,  34 
Platinum  chlorid,  22 
Pleura,  314 
Plexus  chorioidei,  210 
"      climbing,  207 
"      epilemmal,  247 


Plexus,  general  peripheral,  219 

"        hypolemmal,  247 

"        myentericus,  281 

"        myospermaticus,    344 

"        pericapsular,  217 

"        pericellular,  216 

"        submucosus,  281 
Plica  semilunaris,  427 
Plicae  circulares,  270 
Polar  field;  70 
Potash  lye,  23 
Potassium  bichromate,  21 

"  "  acetic  acid,  21,  32 

"  "  formol,  21, 33 

"         permanganate,  24 
Pranter's  resorcin-fuchsin,  26,  43 
Prickle-cells,  79 
Prostate,  345 
Prostatic  crystals,  345 
Protoplasm,  63 
Pyramids  of  Ferrein,  322 
Pyrenin,  65 

R. 

Radial-fibers  of  Miiller,  407 
Reagents,  19 
Rectum,  276 

Reissner's  membrane,  438 
Remak's  fibers,  119 
Renal  corpuscle,  323 
Resorcin-fuchsin,  26,  43 
Resorption  of  bones,  176 
Retia  mirabilia,  143 
Retina,  406 

cerebral  layer,  408 

cone-visual  cells,  411 

fovea,  412 

macula,  412 

neuro-epithelial  layer,  410 

ora   serrata,    414 

pigment  layer,  412 

rod-visual  cells,  411 

technic,  430,  431 

visual  purple,  411 
Rhizoneurons,  190 
Ribbon-cutting,  467 
Ring  cartilages,  311 
Rod-fibers,  411 
Rod-granules,  411 
Rubin  S,  26 
Ruffini's  terminal  cylinder,  225 


Safranin,  25,  41 

Salivary  corpuscles,  261 
glands,  243,  244,  245 

blood-vessels  of,  246 
demilunes,  242,  245,  246 
lymph-vessels  of,  247 
mixed,  244 
mucous,  244 
nerves  of,  247 
serous,  242 
technic,  304,  305 

Salt  solution,  normal,  20 


INDEX. 


483 


Santorini's  duct,  282 
Sarcolemma,   109 
Sarcoplasm,  108 
Sarcous  elements,   108 
Schlussleisten,  79 
Sebaceous  glands,  388 

distribution  of,  389 
secretion  of,  388 
Sebum,  388 

Secretion  collecting  center,  81 
Secretory  capillaries,  86 
Sectioning,  36,  466 

celloidin  objects,  468 

obstacles  in,  and  their  remedy,  467 

paraffin  objects,  466 
Sections,  serial,  466,  469 

preservation  of,  48,  468 
Section-smoother,  467 
Semen,  340 

Seminiferous  tubules,  337 
Sharpey's  fibers,  98,  164 
Silver  nitrate,  22 
Silver  staining,  45 
Sinus  lactiferus,  393 
Sister  loops,  71 
Skin,  373 

arrectores  pilorum,  379 

blood-vessels  of,  390 

coil-glands,  389 

color  of,  376  ' 

corium,  373 

epidermis,  375 

hair-follicles,  378 

hairs,  378 

keratohyaline  granules,  380 

lymph-vessels  of,  391 

nails,  377 

nerves  of,  391 

panniculus  adiposus,  374 

papillae  of,  373 

pigment  of,  376 

sebaceous  glands,  388 

stratum  corneum,  375 

stratum  germinativum,  374 

stratum  granulosum,  376 

stratum  lucidum,  376 

stratum  papillare,  374 

stratum  reticulare,  374 

stratum  subcutaneum,  374 

striated  muscle-fibers  of,  375 

technic,  395,  397 
Slides,  i8 

Smooth  muscle,   104 
Sodium  carminate,  25,  231 
Solitary  follicles,  146,  277 
Spaces  of  Fontana,  406 

"        of  Nuel,  444 
Spatia  zonularia,  423 
Spatium  interfasciale,  423 
Sperm,  340 
Spermatids,  339 
Spermatocytes,  339 
Spermatogenesis,  339 
Spermatogonia,  339 
Spermatosomes,  339 
Spermatofilia,  340 
Spermatozoa,  340 


Spinal  cord,  187 

anterior  column,  188 

anterior  gray  commissure,  189 

anterior  horn,  188 

anterior  median  fissure,  187 

anterior  roots  of  nerves,  189 

astrocytes,   196 

central  canal,  189 

collateral  fibers,  193,  194 

column-cells,  191 

column  of  Burdach,  188 

column  of  Clark,  189 

column  of  Goll,  188 

commissure-cells,   191 

conus  medullaris,  189 

Deiters's  cells,  iq6 

dorsal  nucleus,  189 

ependymal  cells,  195 

funiculus  cuneatus,  188 

funiculus  gracilis,  188 

gelatinous  cortical  layer,  196 

glia-cells,  195 

Golgi's  method  of  staining,  232 

gray  substance  of,  188 

hornspongiosa,   196 

internal  cells,   193 

lateral  column,  188 

lateral  horn,  189 

marginal  cells,  192 

motor  cells,  190 

nerve-fibers  of,  193 

neuroglia,  195 

neuropilem,  189 

plurifunicular  cells,  192 

posterior  column,  188 

posterior  gray  commissure,  189 

posterior  horn,  188 

posterior  roots  of  nerves,  189 

posterior  septum,  188 

reticular  process,  189 

septula  medullaria,  189 

stem-fibers,  192 

substantia  gelatinosa,  189,  197 

substantia  grisea  centralis,  189,  197 

technic,  230,  231,  232 

white  commissure,  188 

white  substance  of,  187,  195 

zona  spongiosa,  189 

zona  terminalis,  189 
Spiral  organ,  44a 
Spleen,  146 

blood-vessels  of,  147,  148 
capsule  of,  147 
ellipsoids,  148 
fibers  of,  150 
intermediate  lacunae,  148 
lobules  of,  152 
lymph-vessels  of,  151 
nerves  of,  151 
nodules  of,  148 
pulp  of,  149 
sheathed  arteries,  148 
technic,  158,  159 
trabeculae  of,  147 
Spongy  bone,  160 
Spontaneous  generation,  68 
Stage-micrometer,  58 


484 


INDEX. 


Staining,  37 

bulk,  40 

chromatin  substance,  40 

connective-tissue  fibrils,  44 

diffuse,  39 

double,  41 

gold,  47 

methylene  blue,  42 

mucus,  42 

nuclear,  38,  39,  41 

of  elastic  fibers,  43 

silver,  45 

triple,  43 

under  the  cover-glass,  53 
Stenon's  duct,  243 
Stomach,  265 

blood-vessels  of,  278 

epithelium  of,  265 

glands  of,  267 

lymph-vessels  of,  280 

membranes  of,  265 

ner\'es  of,  280 

technic,  300 
Strangzellen,  191 
Striated  muscle,  106 
Subarachnoid  space,  211 
Subdural  space.  211 
Sublimate-salt  solution,  22,  35 
Sublingual  gland,  244 
Submaxillary  gland,  245 
Substantia  adamantina,  249 

"  compacta,  160 

"  eburnea,  249 

"  gelatinosa,  189 

"  grisea  centralis,  189 

"  lentis,  417 

"  ossea,  250 

"  reticularis  alba,  201 

"  spongiosa,  160 

Sudoriparous  glands,  389 
Supporting  tissues,  89 
Suprarenal  body,  227 

blood-vessels  of,  229 
cells  of,  228 
cortex  of,  228 
medulla  of,  228 
nerves  of,  230 
technic,  238 
Sutures,  165 
Sweat-glands,  389 
Synarthroses,  165 
Synchondroses,  165 
Syncytium,  67,  73 
Syndesmoses,  165 
Synovia,  168 
Syno\aal  membrane,  167 
Synovial  villi,  167 


Tactile  cells,  221 

"        corpuscles,  224 
Tapetum  cellulosum,  402 

"  fibrosum,  402 

Tarsus,  426 
Taste-buds,  308,  458 


Taste-buds,  gustatory  cells,  459 

nerves  of,  461 

orientation  of,  461 

taste-canal,  459 

taste-pore,  459 

technic,  461 

tegmental  cells,  459 
Tear-glands,  428 

accessory,  426 
Teasing,  29 
Teeth,  248 

cement,  248,  250 

crown,  248 

dental  canaliculi,  249 

dental  cuticle,  250 

dental  fibers,  249 

dental  globules,  249 

dental  ligament,  250 

dental  pulp,  250 

dental  sheaths,  249 

dentine,  249 

development  of,  251 

enamel,  249 

enamel  cuticle,  248 

enamel  prisms,  249 

fang,  248 

interglobular  spaces,  249 

neck,  248 

odontoblasts,  250 

root,  248 

technic,  297 
Telae  chorioides,  210 
Tellyesnickey's  fluid,  21,  32 
Tendons,  183 
Tendon-sheaths,  185 
Tendon-spindle,  225 
Tenon's  space,  423 
Terminal  bars,  79 

"        cylinders,  226 

"        vesicles,  310 
Testis,  336 

ducts  of,  341 

elements  of,  339 

lobules  of,  336 

mediastinum,  336 

nerves  of,  340 

rete,  337 

secretion  of,  340 

seminiferous  tubules,  337 

septula,  336 

technic,  369 

tunica  albuginea  of,  336 

tunica  vasculosa  of,  337 

vessels  of,  340 
Thrombocytes,  139 
Thymus,  317 

atrophy  of,  319 

corpuscles  of,  318 

technic,  321 
Thyro-glossal  duct,  316 
Thyroid  gland,  315 

central  canal  of,  317 
colloid  substance  of,  316 
epithelial  corpuscles  of,  317 
technic,   320 
Tigroid,  115 


INDEX. 


485 


Tissues,  61,  75 

animal,  61 

vegetative,  61 
Tomes's  processes,  255 
Tongue,  257 

glands  of,  261 

lingual  tonsils,  259 

mucosa  of,  257 

muscles  of,  257 

nerves  of,  261 

papillffi  of,  257,  258 

technic,  2g8 

vessels  of,  261 
Tonsils,  lingual,  259 

palatine,  262 

pharyngeal,  262 
Trachea,  309 
Trachoma  glands,  427 
Transitional  epithelium,  330 
Triacid  mixture,  155 
Trophospongium,  64,  116 
Tympanum,  44S 
Tyson's  glands,  389 

U. 

Umbilical  cord,  367,  372 

Ureters,  329 

Urethra,  332 

Urinary  bladder,  330 

Urogenital  sinus,  332 

Uterus,  354 

blood-vessels  of,  358,  361 
cervix,  358 
glands  of,  357 
lymph-vessels  of,  362 
mucosa  of  gravid,  359 
mucosa  of  menstruating,  358 
mucosa  of  virgin  resting,  356 
mucous  crypts,  358 
muscularis  of,  355 
nerves  of,  362 
ovula  Nabothi,  358 
technic,  372 


Vagina,  368 

Valvulse  conniventes,  270 

Van  Gieson's  picrofuchsin,  26,  43 

Vasa  aberrantia,  2S7 

Vasa  vasorum,  135 

Vasoformative  cells,  154 


Vater's  corpuscles,  222 
Veins,  132 

valves  of,  134 
Ventricle  of  Morgagni,  308 
Vermiform  process,  276 
Vesicular  follicle,  351 

cumulus  oophorus,  351 

liquor  folliculi,  35 1 

stratum  granulosum,  351 

theca  folliculi,  35 1 
Vesuvin,  25,  41 
Villi  of  placenta,  365 

of  small  intestine,  271 
synovial,  167 
Visual  purple,  411 
Vitellus,  350 
Vitreous  body,  419 
Vocal  cords,  308 
Volkmann's  canals,  162 
Voluntary  muscle,  106 

W. 

Wagner  and  Meissner's  corpuscles,  224 
Wandering  cells,  93,  137 

hematogenetic,  93 

histogenetic,  93 
Weigert's  hematoxv'lin,  24 

resorcin-fuchsin,  26,  43 
Westphal's  alum-carmine  dahlia,  26 
W^harton's  duct,  245 
Wharton's  jelly,  368 
Wirsung's  duct,  282 
Witches'  milk,  395 


X. 


Xylol,  23,  50 
Xylol-balsam, 
Xvlol,  carbol-. 


23. 
23. 


Zellknoten,  366 
Zenker's  fluid,  21,  33 
Zona  pectinata,  442 
"     pellucida,  350 
"     perforata,  441 
"     tecta,  442 
Zonula  ciliaris,  419 
Zymogen  granules,  283 


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Text-book  of  histology. 

1 

